Geology topics

Whitney Woelmer

Publications and source records attributed to Whitney Woelmer.

7 recordsLinked to original sources

USGS2018

Assessing the influence of watershed characteristics on chlorophyll a in waterbodies at global and regional scales

Prediction of primary production of lentic water bodies (i.e., lakes and reservoirs) is valuable to researchers and resource managers alike, but is very rarely done at the global scale. With the development of remote sensing technologies, it is now feasible to gather large amounts of data across the world, including understudied and remote regions. To determine which factors were most important in explaining the variation of chlorophyll a (Chl- a ), an indicator of primary production in water bodies, at global and regional scales, we first developed a geospatial database of 227 water bodies and watersheds with corresponding Chl- a , nutrient, hydrogeomorphic, and climate data. Then we used a generalized additive modeling approach and developed model selection criteria to select models that most parsimoniously related Chl- a to predictor variables for all 227 water bodies and for 51 lakes in the Laurentian Great Lakes region in the data set. Our best global model contained two hydrogeomorphic variables (water body surface area and the ratio of watershed to water body surface area) and a climate variable (average temperature in the warmest model selection criteria to select models that most parsimoniously related Chl- a to predictor variables quarter) and explained ~ 30% of variation in Chl- a . Our regional model contained one hydrogeomorphic variable (flow accumulation) and the same climate variable, but explained substantially more variation (58%). Our results indicate that a regional approach to watershed modeling may be more informative to predicting Chl- a , and that nearly a third of global variability in Chl- a may be explained using hydrogeomorphic and climate variables.

Inland Waters↗

USGS2017

The contribution of lakes to global inland fisheries harvest

Freshwater ecosystems provide numerous services for communities worldwide, including irrigation, hydropower, and municipal water; however, the services provided by inland fisheries – nourishment, employment, and recreational opportunities – are often comparatively undervalued. We provide an independent estimate of global lake harvest to improve biological and socioeconomic assessments of inland fisheries. On the basis of satellite-derived estimates of chlorophyll concentration from 80,012 globally distributed lakes, lake-specific fishing effort based on human population, and output from a Bayesian hierarchical model, we estimated that the global lake fishery harvest in the year 2011 was 8.4 million tons (mt). Our calculations excluded harvests from highly productive rivers, wetlands, and very small lakes; therefore, the true cumulative global fishery harvest from all freshwater sources likely exceeded 11 mt as reported by the Food and Agriculture Organization of the United Nations (FAO). This putative underestimate by the FAO could diminish the perceived importance of inland fisheries and perpetuate decisions that adversely affect these fisheries and millions of people.

Frontiers in Ecology and the Environment↗

USGS2017

It's like night and day: Diel net-effects on Cercopagidae densities in the Laurentian Great Lakes

In the Laurentian Great Lakes, zooplankters are often sampled using standard ≤153 μm mesh nets without regard to the time of day they are collected. We sampled Cercopagidae during 2013–2014 in northern Lake Huron during day, dusk, and night using two different nets (a 0.5 m wide 153 μm mesh “standard” net and a 0.75 m wide 285 μm mesh “ Bythotrephes ” net) to determine if there were any differences in their sampled densities. Bythotrephes densities with the standard net were approximately 2.07-fold greater when captured at night than during the day. No time of day bias occurred with the Bythotrephes net. Nighttime Bythotrephes densities did not differ between the two net types. Cercopagis densities did not vary with net type or the time of day in this study, but future work should revisit this result given our low sample size and the low occurrence of Cercopagis in Lake Huron. To reduce bias and calculate accurate density estimates, Cercopagidae should be sampled at night if using a standard net or any time of day with the Bythotrephes net. Given the large impact of invasive predatory cladocerans Bythotrephes longimanus and Cercopagis pengoi on food webs since their invasion in the Laurentian Great Lakes in the 1980s, proper estimation of their densities is essential.

Journal of Great Lakes Research↗

USGS2016

The social, economic, and environmental importance of inland fish and fisheries

Though reported capture fisheries are dominated by marine production, inland fish and fisheries make substantial contributions to meeting the challenges faced by individuals, society, and the environment in a changing global landscape. Inland capture fisheries and aquaculture contribute over 40% to the world’s reported finfish production from less than 0.01% of the total volume of water on earth. These fisheries provide food for billions and livelihoods for millions of people worldwide. Herein, using supporting evidence from the literature, we review 10 reasons why inland fish and fisheries are important to the individual (food security, economic security, empowerment), to society (cultural services, recreational services, human health and well-being, knowledge transfer and capacity building), and to the environment (ecosystem function and biodiversity, as aquatic “canaries”, the “green food” movement). However, the current limitations to valuing the services provided by inland fish and fisheries make comparison with other water resource users extremely difficult. This list can serve to demonstrate the importance of inland fish and fisheries, a necessary first step to better incorporating them into agriculture, land-use, and water resource planning, where they are currently often underappreciated or ignored.

Environmental Reviews↗

USGS2015

A new method to generate a high-resolution global distribution map of lake chlorophyll

A new method was developed, evaluated, and applied to generate a global dataset of growing-season chlorophyll- a (chl) concentrations in 2011 for freshwater lakes. Chl observations from freshwater lakes are valuable for estimating lake productivity as well as assessing the role that these lakes play in carbon budgets. The standard 4 km NASA OceanColor L3 chlorophyll concentration products generated from MODIS and MERIS sensor data are not sufficiently representative of global chl values because these can only resolve larger lakes, which generally have lower chl concentrations than lakes of smaller surface area. Our new methodology utilizes the 300 m-resolution MERIS full-resolution full-swath (FRS) global dataset as input and does not rely on the land mask used to generate standard NASA products, which masks many lakes that are otherwise resolvable in MERIS imagery. The new method produced chl concentration values for 78,938 and 1,074 lakes in the northern and southern hemispheres, respectively. The mean chl for lakes visible in the MERIS composite was 19.2 ± 19.2, the median was 13.3, and the interquartile range was 3.90–28.6 mg m −3 . The accuracy of the MERIS-derived values was assessed by comparison with temporally near-coincident and globally distributed in situ measurements from the literature ( n = 185, RMSE = 9.39, R 2 = 0.72). This represents the first global-scale dataset of satellite-derived chl estimates for medium to large lakes.

International Journal of Remote Sensing↗

USGS2015

Status and trends of prey fish populations in Lake Michigan, 2014

The U.S. Geological Survey Great Lakes Science Center has conducted lake-wide surveys of the fish community in Lake Michigan each fall since 1973 using standard 12-m bottom trawls towed along contour at depths of 9 to 110 m at each of seven index transects. The resulting data on relative abundance, size and age structure, and condition of individual fishes are used to estimate various population parameters that are in turn used by state and tribal agencies in managing Lake Michigan fish stocks. All seven established index transects of the survey were completed in 2014. The survey provides relative abundance and biomass estimates between the 5-m and 114-m depth contours of the lake (herein, lake-wide) for prey fish populations, as well as burbot, yellow perch, and the introduced dreissenid mussels. Lake-wide biomass of alewives in 2014 was estimated at 1.6 kilotonnes (kt, 1 kt = 1000 metric tonnes), which was a record low and only 16% of the average biomass estimated since 2005. Moreover, the age distribution of alewives remained truncated with no alewife exceeding an age of 5. Record low biomass was also observed for nearly every other prey fish species: bloater (0.3 kt), rainbow smelt (0.02 kt), slimy sculpin (0.09 kt), deepwater sculpin (1.0 kt) and ninespine stickleback (0.004 kt). Round goby was the only prey fish species to avoid a record-low biomass estimate (2.04 kt); the 2014 estimate was 58% of the average lakewide biomass observed since 2006 when round gobies became relatively abundant in our catches. Burbot lake-wide biomass (0.5 kt in 2014) has remained below 3 kt since 2001. No age-0 yellow perch (i.e., < 100 mm) were captured during the survey, which is indicative of a poor year-class. Lake-wide biomass estimate of dreissenid mussels in 2014 was 23.9 kt, not different from 2013 (23.2 kt). Overall, the total lake-wide prey fish biomass estimate (sum of alewife, bloater, rainbow smelt, deepwater sculpin, slimy sculpin, round goby, and ninespine stickleback) in 2014 was only 5.1 kt, compared to the previous record-low prey fish biomass of 15.2 kt in 2012. In 2014, alewives and round gobies constituted 71% of this total, following a trend of dominance by these species since 2012.

Lake Michigan↗

USGS2014

Status and trends of the Lake Huron offshore Demersal fish community, 1976-2013

The USGS Great Lakes Science Center has conducted trawl surveys to assess annual changes in the offshore demersal fish community of Lake Huron since 1973. Sample sites include five ports in U.S. waters with less frequent sampling near Goderich, Ontario. The 2013 fall bottom trawl survey was carried out between 25 October – 21 November 2013 and included all U.S. ports as well as Goderich, ON. The 2013 main basin prey fish biomass estimate for Lake Huron was 47 kilotonnes, less than half of the estimate in 2012 (97 Kt), and approximately 13 percent of the maximum estimate in the time series. The biomass etimate for YAO alewife in 2013 was lower than in 2012, remained much lower than levels observed before the crash in 2004, and populations were dominated by small fish. Estimated biomass of rainbow smelt also decreased and was the second lowest observed in the time series. Estimated YAO bloater biomass in Lake Huron was also reduced compared to 2012. YOY alewife, rainbow smelt, and bloater abundance and biomass increased over 2012. Biomass estimates for deepwater and slimy sculpins, trout-perch, ninespine stickleback, and round goby in 2013 were lower than in 2012 and remained low compared to historic estimates. Wild juvenile lake trout were captured again in 2013, suggesting that natural reproduction by lake trout continues to occur.

Report↗