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USGS2015

Hydrologic remediation for the Deepwater Horizon incident drove ancillary primary production increase in coastal swamps

As coastal wetlands subside worldwide, there is an urgency to understand the hydrologic drivers and dynamics of plant production and peat accretion. One incidental test of the effects of high rates of discharge on forested wetland production occurred in response to the 2010 Deepwater Horizon incident, in which all diversions in Louisiana were operated at or near their maximum discharge level for an extended period to keep offshore oil from threatened coastal wetlands. Davis Pond Diversion was operated at six times the normal discharge levels for almost 4 months, so that Taxodium distichum swamps downstream of the diversion experienced greater inundation and lower salinity. After this remediation event in 2010, above-ground litter production increased by 2.7 times of production levels in 2007–2011. Biomass of the leaf and reproductive tissues of several species increased; wood litter was minimal and did not change during this period. Root production decreased in 2010 but subsequently returned to pre-remediation values in 2011. Both litter and root production remained high in the second growing season after hydrologic remediation. Annual tree growth (circumference increment) was not significantly altered by the remediation. The potential of freshwater pulses for regulating tidal swamp production is further supported by observations of higher T. distichum growth in lower salinity and/or pulsed environments across the U.S. Gulf Coast. Usage of freshwater pulses to manage altered estuaries deserves further consideration, particularly because the timing and duration of such pulses could influence both primary production and peat accretion.

Louisiana↗

USGS2016

Hydrologic exchanges and baldcypress water use on deltaic hummocks, Louisiana, USA

Coastal forested hummocks support clusters of trees in the saltwater–freshwater transition zone. To examine how hummocks support trees in mesohaline sites that are beyond physiological limits of the trees, we used salinity and stable isotopes ( 2 H and 18 O) of water as tracers to understand water fluxes in hummocks and uptake by baldcypress ( Taxodium distichum (L.) Rich.), which is the most abundant tree species in coastal freshwater forests of the southeastern U.S. Hummocks were always partially submerged and were completely submerged 1 to 8% of the time during the two studied growing seasons, in association with high water in the estuary. Salinity, δ 18 O, and δ 2 H varied more in the shallow open water than in groundwater. Surface water and shallow groundwater were similar to throughfall in isotopic composition, which suggested dominance by rainfall. Salinity of groundwater in hummocks increased with depth, was higher than in swales, and fluctuated little over time. Isotopic composition of xylem water in baldcypress was similar to the vadose zone and unlike other measured sources, indicating that trees preferentially use unsaturated hummock tops as refugia from higher salinity and saturated soil in swales and the lower portions of hummocks. Sustained upward gradients of salinity from groundwater to surface water and vadose water, and low variation in groundwater salinity and isotopic composition, suggested long residence time, limited exchange with surface water, and that the shallow subsurface of hummocks is characterized by episodic salinization and slow dilution.

Louisiana↗

USGS2023

Hydrodynamics and habitat interact to structure fish communities within terminal channels of a tidal freshwater delta

Terminal channels were historically a common feature of tidal delta ecosystems but have become increasingly rare as landscapes have been modified. Tidal hydrodynamics are a defining feature in tidal terminal channel ecosystems from which native aquatic communities have evolved. However, few studies have explored the relationship between fish community structure and hydrodynamics in these tidal terminal channel ecosystems. We sampled fish communities throughout a network of terminal channels within the northeasternmost region of the San Francisco Estuary to determine the relationship between fish community structure and hydrodynamics within these environments. We collected two years (2017 and 2018) of fish community samples using gill nets and analyzed data using multivariate community analyses and count models. We found metrics of fish diversity and counts of native fishes to be greatest upstream (farthest from tidal influence) of the tidal excursion within terminal channels. Counts of non-native fishes were less affected by this hydrodynamic feature of terminal channels and more tightly correlated to local habitat conditions (e.g., water temperature, depth). Our results suggest that channel hydrodynamics plays a role in structuring fish communities within terminal channels, particularly native fishes. These results indicate that hydrodynamics in tidal delta ecosystems may be able to be altered in ways that benefit native fishes without the cost of water pumping.

California↗

USGS2025

Using imaging spectroscopy and elevation in machine learning to estimate soil salinity in intermittently tidal wetlands

Coastal soil salinization patterns are changing due to drought, sea level rise (SLR), and changing freshwater inflow. These changes are expected to impact coastal wetland plant health and ecosystem function, such as changes to biomass and productivity. These impacts have led to greater interest in how we monitor soil salinization across spatial and temporal scales. Remote sensing is a promising tool for estimating soil salinity at the spatial scales required for decision making by land managers. However, the development of a remote sensing estimation approach for wetland soil salinity must account for two factors: (1) the high spatial and temporal heterogeneity of coastal wetlands and (2) the fact that soil salinity is the result of multiple historical land use, hydrological, and geomorphic processes. In spring 2022, a combined airborne-field campaign, known as SHIFT, collected a weekly time series of airborne visible to shortwave infrared (VSWIR) image spectroscopy data. This dataset provides a unique opportunity to assess the application of fine spatial (5 m) and temporal (weekly) resolution VSWIR data to estimate root zone soil salinity; when combined with environmental variables such as elevation, these data can account for some of these factors. In this study, we utilized VSWIR and elevation datasets in a random forest regression to predict and map soil salinity in an intermittently tidal estuary, Devereux Slough, located in Santa Barbara County, California. The final model combined spectral indices with elevation to better capture soil salinity dynamics despite lower correlation ( r = 0.85) than solely using elevation ( r = 0.92). This research demonstrates the utility of remote sensing datasets, namely, elevation and the modified Anthocyanin Reflectance Index (mARI), for predicting root zone soil salinity in intermittently tidal coastal wetlands. These findings are an important step in advancing coastal remote sensing by creating a gridded salinity dataset that can be used for salinity monitoring and other coastal applications, such as modeling change in vegetation communities or ecosystems facing the impacts of climatic variability and change.

California↗

USGS2017

Host density increases parasite recruitment but decreases host risk in a snail-trematode system

Most species aggregate in local patches. High host density in patches increases contact rate between hosts and parasites, increasing parasite transmission success. At the same time, for environmentally-transmitted parasites, high host density can decrease infection risk to individual hosts, because infective stages are divided among all hosts in a patch, leading to safety in numbers. We tested these predictions using the California horn snail, Cerithideopsis californica (=Cerithidea californica), which is the first intermediate host for at least 19 digenean trematode species in California estuaries. Snails become infected by ingesting trematode eggs or through penetration by free-swimming miracidia that hatch from trematode eggs deposited with final-host (bird or mammal) feces. This complex life cycle decouples infective-stage production from transmission, raising the possibility of an inverse relationship between host density and infection risk. In a field survey, higher snail density was associated with increased trematode (infected snail) density, but decreased trematode prevalence, consistent with either safety in numbers, parasitic castration, or both. To determine the extent to which safety in numbers drove the negative snail density-trematode prevalence association, we manipulated uninfected snail density in 83 cages at eight sites within Carpinteria Salt Marsh (CA, USA). At each site, we quantified snail density and used data on final-host (bird and raccoon) distributions to control for between-site variation in infective-stage supply. After three months, overall trematode infections per cage increased with snail-biomass density. For egg-transmitted trematodes, per-snail infection risk decreased with snail-biomass density in the cage and surrounding area, whereas per-snail infection risk did not decrease for miracidium-transmitted trematodes. Furthermore, both trematode recruitment and infection risk increased with infective-stage input, but this was significant only for miracidium-transmitted species. A model parameterized with our experimental results and snail densities from 524 field transects estimated that safety in numbers, when combined with host aggregation, halved per-capita infection risk in this snail population. We conclude that, depending on transmission mode, host density can enhance parasite recruitment and reduce per-capita infection risk.

Ecology↗

USGS2019

A strong colonizer rules the trematode guild in an intertidal snail host

We examined the extent to which supply‐side, niche, and competition theories and concepts help explain a trematode community in which one species comprises 87% of the trematode individuals, and the remaining 15 species each have <3%. We collected and dissected the common and wide‐ranging snail host Heleobia australis over four seasons from three distinct habitats from the intertidal area of the Bahía Blanca estuary, Argentina. Inside a snail, trematodes interact with each other with outcomes that depend on facilitation, competition, and preemption, suggesting that dominant species should be common. The abundant trematode species, Microphallus simillimus , is a weak competitor , but has life‐history traits and strategies associated with higher colonization ability that could increase its probability of invading the host first, allowing it to preempt the rare species. Rather than segregate by habitat, trematode species aggregated in pans during the summer where dominant trematode species often excluded subordinate ones. Despite losses to competition, and a lack of niche partitioning, M. simillimus ruled this species‐rich trematode guild through strong recruitment and (potentially) preemption. Therefore, extremely skewed species abundance distributions, like this one, can derive from extremely skewed colonization abilities.

Bahia Blanca Estuary↗

USGS2024

A comparison of eDNA sampling methods in an estuarine environment on presence of longfin smelt (Spirinchus thaleichthys) and fish community composition

The loss of tidal wetlands in the San Francisco Bay estuary have led to declines in native fish presence. Restoration of tidal wetlands in this area has intensified, with a primary goal of increasing the number of native fishes. We compared the presence of longfin smelt in naturally accreted and beneficial dredge reuse wetlands as a measure of successful restoration. We used environmental DNA (eDNA) analyses as our metric for fish presence and fish community composition, employing two different water sampling methods for comparison (standard and high-volume). Longfin smelt were present in multiple sites, but at numbers too low for accurate comparisons across sites. Community composition varied based on the water sampling method, but the presence/absence of longfin smelt was consistent across sampling methods. As this represents a pilot study, further refinement of methodology is necessary, but the use of high-volume water sampling methods is promising.

California↗

USGS2010

Accumulation of current-use and organochlorine pesticides in crab embyros from northern California, USA

Invertebrates have long been used as resident sentinels for assessing ecosystem health and productivity. The shore crabs, Hemigrapsus oregonensis and Pachygrapsus crassipes, are abundant in estuaries and beaches throughout northern California, USA and have been used as indicators of habitat conditions in several salt marshes. The overall objectives of the present study were to conduct a lab-based study to test the accumulation of current-use pesticides, validate the analytical method and to analyze field-collected crabs for a suite of 74 current-use and legacy pesticides. A simple laboratory uptake study was designed to determine if embryos could bioconcentrate the herbicide molinate over a 7-d period. At the end of the experiment, embryos were removed from the crabs and analyzed by gas chromatography/mass spectrometry. Although relatively hydrophilic (log K(OW) of 2.9), molinate did accumulate with an estimated bioconcentration factor (log BCF) of approximately 2.5. Following method validation, embryos were collected from two different Northern California salt marshes and analyzed. In field-collected embryos 18 current-use and eight organochlorine pesticides were detected including synthetic pyrethroids and organophosphate insecticides, as well as DDT and its degradates. Lipid-normalized concentrations of the pesticides detected in the field-collected crab embryos ranged from 0.1 to 4 ppm. Pesticide concentrations and profiles in crab embryos were site specific and could be correlated to differences in land-use practices. These preliminary results indicate that embryos are an effective sink for organic contaminants in the environment and have the potential to be good indicators of ecosystem health, especially when contaminant body burden analyses are paired with reproductive impairment assays.

California↗

USGS1996

Sediment quality assessment studies of Tampa bay, Florida

A survey of the toxicity of sediments throughout the Tampa Bay estuary was performed as part of the National Oceanic and Atmospheric Administration's National Status and Trends Program. The objectives of the survey were to determine the spatial extent and severity of toxicity and to identify relationships between chemical contamination and toxicity. Three independent toxicity tests were performed: a 10-d amphipod survival test of the whole sediments with Ampelisca abdita , a sea urchin fertilization test of sediment pore water with Arbacia punctulata , and a 5-min Microtox® bioluminescence test with solvent extracts of the sediments. Seventy-three percent of the 165 undiluted sediment pore-water samples were significantly toxic relative to reference samples with the sea urchin fertilization test. In contrast, only 2% of the 165 samples were significantly toxic in the amphipod tests. The causes of toxicity were not determined. However, concentrations of numerous trace metals, pesticides, polychlorinated biphenyl (PCB) congeners, polycyclic aromatic hydrocarbons (PAHs), and ammonia were highly correlated with pore-water toxicity. Concentrations of many substances, especially total dichlorodiphenyltrichloroethanes (DDTs), endrin, total PCBs, certain PAHs, lead, and zinc, occurred at concentrations in the toxic samples that equaled or exceeded concentrations that have been previously associated with sediment toxicity.

Florida↗

USGS2000

Impact of storm-water outfalls on sediment quallity in corpus Christi Bay, Texas, USA

To determine the quality of sediments and extent of contaminant impacts, a Sediment Quality Triad (SQT) study was conducted at 36 sites in the Corpus Christi Bay, Texas, USA, system. Fifteen of the 36 sites were located near storm-water outfalls, but 13 other sites (i.e., industrial and domestic outfalls, oil field–produced water discharges, and dredging activity) and eight reference sites were also evaluated. Sediment samples were collected and analyzed for physical–chemical characteristics, contaminant concentrations (metals, polycyclic aromatic hydrocarbons [PAHs], polychlorinated biphenyls [PCBs], and pesticides), toxicity (amphipod and mysid solid phase and sea urchin pore-water fertilization and embryological development tests), and a benthic index of biotic integrity (BIBI) composed of 10 independent metrics calculated for each site. This large data matrix was reduced using multivariate analysis to create new variables for each component representing overall means and containing most of the variance in the larger data set. The new variables were used to conduct the correlation analysis. Toxicity was significantly correlated with both chemistry and ecological responses, whereas no correlations between the benthic metrics and sediment chemistry were observed. Using the combined information from the SQT, four of the five most degraded sites were storm-water outfall sites. Although estuaries are naturally stressful environments because of salinity and temperature fluctuations, this ecosystem appears to have been compromised by anthropogenic influences similar to what has been observed for other heavily urbanized bay systems along the Texas and Gulf coast.

Texas↗

USGS2000

Quantifying solar spectral irradiance in aquatic habitats for the assessment of photoenhanced toxicity

The spectra and intensity of solar radiation (solar spectral irradiance [SSI]) was quantified in selected aquatic habitats in the vicinity of an oil field on the California coast. Solar spectral irradiance measurements consisted of spectral scans (280–700 nm) and radiometric measurements of ultraviolet (UV): UVB (280–320 nm) and UVA (320–400 nm). Solar spectral irradiance measurements were taken at the surface and at various depths in two marsh ponds, a shallow wetland, an estuary lagoon, and the intertidal area of a high-energy sandy beach. Daily fluctuation in SSI showed a general parabolic relationship with time; maximum structure–activity relationship (SAR) was observed at approximate solar noon. Solar spectral irradiance measurements taken at 10-cm depth at approximate solar noon in multiple aquatic habitats exhibited only a twofold variation in visible light and UVA and a 4.5-fold variation in UVB. Visible light ranged from 11,000 to 19,000 μW/cm 2 , UVA ranged from 460 to 1,100 μW/cm 2 , and UVB ranged from 8.4 to 38 μW/cm 2 . In each habitat, the attenuation of light intensity with increasing water depth was differentially affected over specific wavelengths of SSI. The study results allowed the development of environmentally realistic light regimes necessary for photoenhanced toxicity studies.

Environmental Toxicology and Chemistry↗

USGS2000

Evaluation of planar halogenated and polycyclic aromatic hydrocarbons in estuarine sediments using ethoxyresorufin-O-deethylase induction of H4IIE cells

Polycyclic aromatic hydrocarbons (PAHs) and planar halogenated hydrocarbons (PHHs), including polychlorinated dibenzo- p -dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) were determined in fractionated sediment extracts from the Hudson-Raritan estuary and Newark Bay, New Jersey, USA, as part of a comprehensive risk assessment. Contributions of PCDDs/PCDFs, PCBs, and PAHs to the total toxic equivalents (TEQs) were measured using an H4IIE bioassay and calculated from instrumentally determined concentrations using international toxic equivalency factors. The H4IIE TEQs of whole and fractionated extracts were compared to calculated TEQs to investigate the applicability of the bioassay approach for evaluating 7-ethoxyresorufin- O -deethylease induction by PHHs and PAHs present together in complex mixtures. Although 2,3,7,8-tetrachloro-dibenzo- p -dioxin contributed from 41 to 79% of the calculated TEQs from PCDDs/PCDFs and planar PCBs in all sediments sampled, the PAH-containing fractions accounted for >80% of the total TEQs determined either instrumentally or by bioassay. Calculated TEQs from PAHs, based on reported toxic equivalency factors for only seven PAHs, were severalfold greater than the bioassay-derived TEQs of PAH-only fractions of the sediment extracts. Significant correlations were observed between bioassay and instrumentally determined toxic equivalents in the more purified fractions but not in fractions only purified by size-exclusion or argentate chromatographies alone.

Environmental Toxicology and Chemistry↗

USGS2020

Applying cumulative effects to strategically advance large‐scale ecosystem restoration

International efforts to restore degraded ecosystems will continue to expand over the coming decades, yet the factors contributing to the effectiveness of long‐term restoration across large areas remain largely unexplored. At large scales, outcomes are more complex and synergistic than the additive impacts of individual restoration projects. Here, we propose a cumulative‐effects conceptual framework to inform restoration design and implementation and to comprehensively measure ecological outcomes. To evaluate and illustrate this approach, we reviewed long‐term restoration in several large coastal and riverine areas across the US: the greater Florida Everglades; Gulf of Mexico coast; lower Columbia River and estuary; Puget Sound; San Francisco Bay and Sacramento–San Joaquin Delta; Missouri River; and northeastern coastal states. Evidence supported eight modes of cumulative effects of interacting restoration projects, which improved outcomes for species and ecosystems at landscape and regional scales. We conclude that cumulative effects, usually measured for ecosystem degradation, are also measurable for ecosystem restoration. The consideration of evidence‐based cumulative effects will help managers of large‐scale restoration capitalize on positive feedback and reduce countervailing effects.

Gulf of Mexico, San Francisco Bay/Sacramento Delta↗

USGS2018

Explicit consideration of preferential groundwater discharges as surface water ecosystem control points

Heterogeneities in sediment and rock permeability induce preferentialgroundwater flow from the scale of pore networks to large basins. Inthe unsaturated zone, preferential flow is frequently conceptualizedas an infiltration process dominated by macropores, resulting in stron-ger delivery of surface‐derived solute than would be predicted via dif-fuse percolation alone (Beven & Germann, 2013). In the saturatedzone, preferential flow occurs in bedrock fractures and karst, alonggeologic contacts and fault zones, and through unconsolidated mate-rials of relatively high connectivity (Winter, Harvey, Franke, & Alley,1998). Focused flow paths emanate on the land surface as preferentialgroundwater discharges, observed throughout stream, lake, wetland,and estuary systems. The prevalence, and perhaps dominance, of spa-tially focused discharges to surface water contrasts with the spatiallydiffuse flow often assumed in various conceptual and predictiveprocess‐based models. This simplification is not made out of anunawareness of preferential groundwater discharge; rather, the abilityto reliably measure focused flow across a range of scales is hamperedby a reliance on (relatively) sparse point measurements. Additionally,realistic distributions of <1‐ to 100‐m‐scale preferential groundwaterdischarges are computationally expensive to simulate at scales rele-vant to decision making. If we accept that preferential discharge ofgroundwater to surface water is an ubiquitous process, fundamentalquestions facing contemporary hydrogeology include (a) When doesspatially focused groundwater discharge matter to the process wewould like to predict? Followed by (b) If we determine when preferen-tial discharge “matters” and should not be simplified to diffuse inflows,how do we measure it at the spatial and temporal scales needed toinform process‐based models?

Hydrological Processes↗

USGS2018

Spatial distribution of band recoveries of black brant

On average, band recovery rates of adult black brant ( Branta bernicla nigricans ) more than doubled between the 2000s and 2010s. However, the spatial distribution of band recoveries of black brant has not been reported. Our objective was to describe the spatial distribution of band recoveries of black brant since 1990. We found that Alaska, California, and Mexico accounted for ≥89% of band recoveries for black brant released from the Arctic and the Tutakoke River Colony in southwestern Alaska, in each decade studied. Although recovery rates increased in each major harvest region from the 1990s to 2010s, increases were not even. For brant released from the Arctic, the recovery rate in Alaska has gone up 7‐fold, whereas the recovery rate in Mexico has increased 1.3‐fold since the 1990s. For brant banded in the Arctic, the increased recovery rates in Alaska resulted largely from a rise in recoveries from the Izembek Lagoon area. For brant banded at the Tutakoke River Colony, the recovery rate in Alaska increased 4.8‐fold, whereas recovery rates in Mexico increased 1.6‐fold. Despite the reduced relative contribution of Mexico to band recoveries in the 2010s, Bahia San Quintin, Mexico, still contributes more recoveries than any other wintering estuary. Because 57–60% of black brant band recoveries occur at the localities of Izembek Lagoon, Alaska; Humboldt Bay, California; and Bahia San Quintin, it is likely that accurate annual estimates of the black brant population using Lincoln's method could be derived from hunter bag checks at these 3 areas. If population managers are interested in managing harvest rates of black brant, they could focus efforts on the main hunting areas we highlight in this paper. Finally, it is unclear if the recent increases in band recovery rates are the result of increased harvest, a declining population, or both; therefore, we suggest refinement of population monitoring programs and continued monitoring of band recovery rates.

Journal of Wildlife Management↗

USGS2021

Habitat features predict carrying capacity of a recovering marine carnivore

The recovery of large carnivore species from over‐exploitation can have socioecological effects; thus, reliable estimates of potential abundance and distribution represent a valuable tool for developing management objectives and recovery criteria. For sea otters ( Enhydra lutris ), as with many apex predators, equilibrium abundance is not constant across space but rather varies as a function of local habitat quality and resource dynamics, thereby complicating the extrapolation of carrying capacity ( K ) from one location to another. To overcome this challenge, we developed a state‐space model of density‐dependent population dynamics in southern sea otters ( E. l. nereis ), in which K is estimated as a continuously varying function of a suite of physical, biotic, and oceanographic variables, all described at fine spatial scales. We used a theta‐logistic process model that included environmental stochasticity and allowed for density‐independent mortality associated with shark bites. We used Bayesian methods to fit the model to time series of survey data, augmented by auxiliary data on cause of death in stranded otters. Our model results showed that the expected density at K for a given area can be predicted based on local bathymetry (depth and distance from shore), benthic substrate composition (rocky vs. soft sediments), presence of kelp canopy, net primary productivity, and whether or not the area is inside an estuary. In addition to density‐dependent reductions in growth, increased levels of shark‐bite mortality over the last decade have also acted to limit population expansion. We used the functional relationships between habitat variables and equilibrium density to project estimated values of K for the entire historical range of southern sea otters in California, USA, accounting for spatial variation in habitat quality. Our results suggest that California could eventually support 17,226 otters (95% CrI = 9,739–30,087). We also used the fitted model to compute candidate values of optimal sustainable population abundance (OSP) for all of California and for regions within California. We employed a simulation‐based approach to determine the abundance associated with the maximum net productivity level (MNPL) and propose that the upper quartile of the distribution of MNPL estimates (accounting for parameter uncertainty) represents an appropriate threshold value for OSP. Based on this analysis, we suggest a candidate value for OSP (for all of California) of 10,236, which represents 59.4% of projected K .

California↗

USGS2014

Recent population size, trends, and limiting factors for the double-crested Cormorant in Western North America

The status of the double-crested cormorant ( Phalacrocorax auritus ) in western North America was last evaluated during 1987–2003. In the interim, concern has grown over the potential impact of predation by double-crested cormorants on juvenile salmonids ( Oncorhynchus spp.), particularly in the Columbia Basin and along the Pacific coast where some salmonids are listed for protection under the United States Endangered Species Act. Recent re-evaluations of double-crested cormorant management at the local, flyway, and federal level warrant further examination of the current population size and trends in western North America. We collected colony size data for the western population (British Columbia, Washington, Oregon, Idaho, California, Nevada, Utah, Arizona, and the portions of Montana, Wyoming, Colorado and New Mexico west of the Continental Divide) by conducting aircraft-, boat-, or ground-based surveys and by cooperating with government agencies, universities, and non-profit organizations. In 2009, we estimated approximately 31,200 breeding pairs in the western population. We estimated that cormorant numbers in the Pacific Region (British Columbia, Washington, Oregon, and California) increased 72% from 1987–1992 to circa 2009. Based on the best available data for this period, the average annual growth rate (λ) of the number of breeding birds in the Pacific Region was 1.03, versus 1.07 for the population east of the Continental Divide during recent decades. Most of the increase in the Pacific Region can be attributed to an increase in the size of the nesting colony on East Sand Island in the Columbia River estuary, which accounts for about 39% of all breeding pairs in the western population and is the largest known breeding colony for the species (12,087 breeding pairs estimated in 2009). In contrast, numbers of breeding pairs estimated in coastal British Columbia and Washington have declined by approximately 66% during this same period. Disturbance at breeding colonies by bald eagles ( Haliaeetus leucocephalus ) and humans are likely limiting factors on the growth of the western population at present. Because of differences in biology and management, the western population of double-crested cormorants warrants consideration as a separate management unit from the population east of the Continental Divide.

Journal of Wildlife Management↗

USGS2017

A river-scale Lagrangian experiment examining controls on phytoplankton dynamics in the presence and absence of treated wastewater effluent high in ammonium

Phytoplankton are critical component of the food web in most large rivers and estuaries, and thus identifying dominant controls on phytoplankton abundance and species composition is important to scientists, managers, and policymakers. Recent studies from a variety of systems indicate that ammonium ( NH + 4 ) in treated wastewater effluent decreases primary production and alters phytoplankton species composition. However, these findings are based mainly on laboratory and enclosure studies, which may not adequately represent natural systems. To test effects of effluent high in ammonium on phytoplankton at the ecosystem scale, we conducted whole-river–scale experiments by halting discharges to the Sacramento River from the regional wastewater treatment plant (WWTP), and used a Lagrangian approach to compare changes in phytoplankton abundance and species composition in the presence (+EFF) and absence (−EFF) of effluent. Over 5 d of downstream travel from 20 km above to 50 km below the WWTP, chlorophyll concentrations declined from 15–25 to ∼2.5 μg L −1 , irrespective of effluent addition. Benthic diatoms were dominant in most samples. We found no significant difference in phytoplankton abundance or species composition between +EFF and −EFF conditions. Moreover, greatest declines in chlorophyll occurred upstream of the WWTP where NH + 4 concentrations were low. Grazing by clams and zooplankton could not account for observed losses, suggesting other factors such as hydrodynamics and light limitation were responsible for phytoplankton declines. These results highlight the advantages of conducting ecosystem-scale, Lagrangian-based experiments to understand the dynamic and complex interplay between physical, chemical, and biological factors that control phytoplankton populations.

California↗