Geology topics
Leandro E. Miranda
Publications and source records attributed to Leandro E. Miranda.
Aging, climate, and invasions threaten reservoirs in the Mississippi basin
Reservoirs in the Mississippi River basin are facing three momentous threats. The first two, aging and climate change, are relatively slow moving and their signal can be hard to discern given their stretched temporal scales. The third, species invasions, is faster paced and discernable within shorter temporal scales and restricted spatial scales. Aging and climate directly affect reservoir environments and indirectly affect their biotic communities. Climate change is expected to interact with aging to speed up and, in some instances, slow down aging. Conversely, invasions primarily imperil biotic communities but can also impact environmental elements. This triple jeopardy is expected to transform reservoir environs and their biotic assemblages in various, often uncertain, ways. I take a broad view of these threats within the Mississippi River basin. A basin-scale perspective, in contrast to a single reservoir or regional scale, may enhance awareness of reservoirs at a larger level and produce understanding less evident at local levels, hence possibly offering a wider range of choices for confronting threats. My aim is to (1) provide a synopsis of the assemblage of reservoirs and their attributes over the Mississippi River basin, (2) describe the issues related to aging, climate change, and invasions, and (3) consider a conservation framework for confronting these pressures. Given the overlapping temporal, spatial, and ecological effects of these threats, it is essential to address their effects simultaneously.
Fish life-history traits predict abundance-occupancy patterns in artificial lakes
Life-history traits of a species have been postulated as a factor in abundance and occupancy patterns. Understanding how traits contribute to the ubiquity and rarity of taxa can facilitate the development of effective conservation policy by establishing a connection between species requirements and resource. The goal was to evaluate fish assemblages in artificial lakes for evidence of the abundance-occupancy patterns reported in natural environments and, if evident, to explore if observed patterns of abundance and occupancy could be attributed to species traits. Fish abundance and occupancy were estimated over 1990–2018 in 22 artificial lakes impounded within the Tennessee River basin, USA. Consistent with reports for many other taxonomic groups in natural environments, there was a positive association amidst 114 fish species between abundance and occupancy in artificial lakes ( R 2 = 0.78). This result indicates that the fish assemblages that develop in these anthropized environments follow the fundamental abundance-occupancy patterns uncovered in natural environments, despite assemblages having been disfigured by the dramatic rearrangement of habitats brought by impoundment. Moreover, a redundancy analysis focusing mostly on reproductive and habitat traits adequately predicted abundance-occupancy patterns of fish assemblages in artificial lakes ( R 2 = 0.69). Species abundance-occupancy is influenced by the interplay between life-history traits and habitat availability, even in artificial lakes, and by extension, possibly other artificial ecosystems.
Influence of invasive bigheaded carps on abundance of Gizzard Shad in the Tennessee River
Objective The Tennessee River basin and its cascade of reservoirs are home to some of the most diverse freshwater fish assemblages in the world. This unique system is threatened by the ongoing invasion of Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis , hereafter referred to together as “bigheaded carps.” Bigheaded carps may directly compete for food resources with native clupeid species such as Gizzard Shad Dorosoma cepedianum , and this potential interaction could have damaging ecological and economic consequences. High relative abundances of Gizzard Shad are crucial to the Tennessee River food web and associated fisheries because of their role as a forage base for piscivorous species. Methods We analyzed a collection of annual gillnetting and electrofishing data spanning from 1990 to 2017 to test whether Gizzard Shad relative abundances have changed in Tennessee River reservoirs since the arrival of bigheaded carps. Result Our analyses indicated that Gizzard Shad abundances have been declining but were already declining prior to the arrival of bigheaded carps in the Tennessee River. Conclusion At this stage in the invasion, we could not attribute a cause-and-effect relationship to the inverse correlation between Gizzard Shad and bigheaded carps, but we advise continued monitoring of indicators of harmful interactions.
Impact of dams on stream fish diversity: A different result
Impoundments can drastically change the physical and biological characteristics of fluvial systems. Changes in the physical characteristics, such as reductions in flow, increased sediment deposition, and increased surface area, often influence the system’s biological components, including plant, macroinvertebrate, and fish assemblages. In addition to having direct effects on impounded waterbodies, impoundments can also have wide-ranging effects at the watershed scale, particularly on upstream tributary streams. The purpose of this study was to assess the magnitude of these effects. We analyzed historical data from 26 streams distributed across five sub-basins in the Bluff Hills region of the Yazoo Basin, MS, USA. All five major tributary rivers in this region are impounded by large (11,240–26,143 hectares) reservoirs for flood control. We compared fish assemblages in streams located upstream and downstream of the four reservoirs using PERMANOVA, and contrary to expectations, we found no significant differences between the upstream and downstream assemblages. We explore several possible explanations for this discrepancy and suggest that stream assemblage response to impoundment may be nuanced by the regional species pool, the history of stream conditions in the watershed, and the resistance of the streams to periodic disturbances.
Facing our freshwater crisis via fluid and agile communication: A grand challenge
Earth has been labeled the blue planet because of its abundance of water that covers most of its surface, but the majority is salt water in our oceans. Oceans account for ~352 million km 2 or 69% of the planet's surface, land for 150 million km 2 or 29%, and fresh water for 9 million km 2 or 2% ( Shiklomanov, 2000 ). Most of the fresh water is locked away in glaciers and ice sheets on Greenland and Antarctica, with less than a third accessible to biota ( Shiklomanov, 2000 ). This miniscule fraction of fresh water is our most precious natural resource, the foundation for life in terrestrial environments, and humanity depends on it, but the resource faces enormous threats. My aim in this brief editorial is to define the freshwater resource, succinctly summarize the major threats it faces, and underscore recent calls for conservation. My review is cursory, but I call attention to various recent exhaustive reviews. I end with my views on how journals can help advance global freshwater conservation efforts.
Fish functional gradients along a reservoir cascade
1.The transformations of fish assemblages caused by reservoir cascades can be severe at the reach scale, but basin-scale effects are less clear. However, prevailing river concepts provide a framework for predicting basin-scale effects. 2. To determine if predictions made by the River Continuum Concept relative to the function of fish assemblages are sustained in a temperate river transformed into a reservoir cascade, we examined longitudinal trends in the distribution of fish functional traits over 23 reservoirs of the Tennessee River, USA. 3. In all, 115 species were recorded representing 62 traits, with trait richness increasing longitudinally in a downstream direction. Trophic, reproductive, and habitat traits showed various increasing and decreasing patterns up and down the reservoir cascade. The observed gradients in trait richness and trait distributions were generally consistent with those expected in unregulated rivers, with few unexpected results. 4. The transformation of lotic systems into lentic ones has changed habitats and sources of food and encouraged the proliferation of certain feeding (e.g., detritivores, planktivores, invertivores, piscivores), reproduction (e.g., nest spawners polyphils, broadcast spawners phytolithophils), and habitat (slow current, lacustrine, large river) traits. In essence, reservoirs have expanded downstream habitats in an upstream direction, and thus allowed upstream expansion of species and traits that would have normally not been well represented in upper reaches of the Tennessee River basin. Nevertheless, the impounded Tennessee River has maintained much of its functional integrity, despite extensive alterations to the riverscape. 5. We suggest that while reservoirs have been shown to have major local-scale effects on riverine fish assemblages, with access to riverine habitats, and with proactive conservation strategies, fish functional richness can remain remarkably high at the basin scale.
Evaluating regional length limits in freshwater fisheries
Length limits are often used in recreational fisheries management to prevent overharvest and manipulate fish size distributions. These regulations are ideally customized to meet water-specific stock dynamics and fishery objectives. However, in districts with numerous discrete waters, fisheries are commonly managed with a universal regional regulation. Evaluating alternative regional length limits requires consideration of management objectives that may not be important at the single-system level but that emerge as relevant at the regional scale, such as uniformity of regional harvest, diversity of average catch sizes, and opportunity to harvest. We developed a flexible tool for evaluating regional length limits. The tool joins the well-established Beverton–Holt yield-per-recruit model with elements of decision-support methods. The model quantifies regional management objectives as utility functions that are weighted and summed into a single value used to evaluate alternative length limits. The flexibility of the tool stems from its capacity to consider a mixture of stock parameters and associated uncertainty to evaluate multiple length limits, weighting an array of regional fishery objectives quantified by various performance metrics. This adjustability affords flexibility to consider a diversity of options that can stimulate innovation in setting regional length limits. We demonstrate the model by evaluating varying length limits on fishery objectives related to the management of hypothetical yellow perch ( Perca flavescens ) populations and real black crappie ( Pomoxis nigromaculatus ) populations.
Patterns of zero and nonzero counts suggest spatiotemporal distributions, aggregation, and dispersion of invasive carp
Bigheaded carp Hypophthalmichthys spp. are invasive species native to Asia expanding in the Mississippi River Basin in North America. An understanding of spatiotemporal distribution and aggregation of invasive carp is key to establishing when and where to focus surveillance designed to monitor expansion, and to managing harvest programs designed to curb population densities. We applied a two-stage hurdle model to assess three aspects of bigheaded carp ecology: distribution, relative abundance, and aggregation. Stage 1 was a binary 0/1 model that represented fish presence (p), and stage 2 was a truncated count distribution that had no zeros and included counts ≥ 1 only (C). Estimates of p and C varied temporally and spatially, but not in harmony and sometimes in opposing directions, indicating temporal and spatial swings in fish distributions and aggregations. Intense fish aggregations in channels in spring shown by low p’s and high C’s, eventually scattered by summer and fall as shown by high p’s and low C’s. An alternative but complementary interpretation of our observations is that p indexes incidence of aggregations and C indexes size of aggregations. Partitioning catch into its zero and nonzero components provided insight into population ecology that can inform development of monitoring and management of harvesting programs targeted at lessening potential effects of the invasion.
Abundance-occupancy patterns of black bass in an impounded river
A positive relationship has been documented for a wide diversity of taxa between the percentage of transects sampled in which a species is recorded (i.e., occupancy) and the average abundance of the species at transects where recorded. This positive relationship implies that abundance increases faster than occupancy, so populations that occupy more sites also tend to occupy them at higher abundances. Plainly, there is a limit to the sites available for a species to occupy, so as the population expands numerically, abundance at a site must also increase. The pattern may differ across species and geography depending on aspects such as species vital rates, resource use, and resource availability. I investigated abundance–occupancy patterns of three black basses Micropterus spp. in reservoirs of the mainstem Tennessee River, USA. The data set included relative abundance estimates made at 7,237 sites in nine reservoirs sampled during 1997–2018, for 43,243 black bass, including 67% Largemouth Bass Micropterus salmoides , 14% Smallmouth Bass M. dolomieu , and 19% Spotted Bass M. punctulatus . As relative abundance increased due to natural annual population fluctuations, occupancy also increased, but faster for Largemouth Bass and more slowly for Smallmouth Bass and Spotted Bass. Largemouth Bass spread abundance more thinly over many sites, and Smallmouth Bass and Spotted Bass spread abundance more thickly over fewer sites. The recognition that black bass populations that decline in occupancy face the additional burden of disproportionally larger decreases in abundance per site, or that black bass that decline in abundance per site face decreases in occupancy, has various conservation and habitat management implications.
Climate change alters aging patterns of reservoir aquatic habitats
Two slow-moving developments are threatening reservoir aquatic habitats globally: aging and climate change. These events are projected to transform reservoir aquatic habitats in various and often unpredictable ways. Aging affects in-lake habitats directly, whereas climate change affects both in-lake and off-lake conditions. Climate change is expected to accelerate and, in some instances, possibly decelerate aging. Aging can be indexed as functional age, an index that signals the position of a reservoir along its lifespan relying on in-lake descriptors of aquatic habitat. Using existing habitat datasets and climate projections, we developed semi-quantitative predictions about the effect of climate change on reservoir functional age in the USA. Driven by increased warming, functional age was predicted to increase latitudinally from south to north with no obvious longitudinal gradient. Functional age also changed with precipitation, increasing latitudinally from south to north and longitudinally in the east and west but decreasing in the central USA. Our projections are tentative because of the uncertain nature of reservoir aging and climate change sciences, as well as the inexactness of available data and models. We review general strategies suitable for systematically dealing with the unpredictable and constantly changing conditions expected to occur this century as reservoirs certainly continue to get older, within the scope of uncertain climate change projections.
Reservoir attributes display cascading spatial patterns along river basins
Considering reservoirs as linear fragments in a basin's river network could improve understanding, predictability, and management efficiency. We looked for general cascading spatial patterns across five categories of reservoir attributes: land cover, morphology and hydrology, fish habitat, fish assemblages, and fisheries. Attributes were pulled from various databases for large reservoirs (>100 ha) located in the United States. 16 widely distributed river basins, each including a minimum of 15 large reservoirs, were selected for analysis. Using analysis of covariance with basin as the class variable, we tested each attribute as a linear function of catchment area, which is an index of reservoir position in the basin. The majority of reservoir attributes displayed log-linear patterns as catchment area increased, indicating that reservoirs act as members of a larger network just as river reaches do. Several patterns were detected including attributes with no apparent lengthwise arrangement along the basin; cascading spatial patterns in which attributes increase or decrease from upstream to downstream within a basin; and attributes that increase with catchment area in some basins, decrease in others, or may simply remain constant throughout the basin. We conclude that each pattern may have different implications for management, and that the effectiveness with which most management activities influence reservoirs is likely to increase or decrease along river basins.
Supplemental habitat is reservoir dependent: Identifying optimal planting decision using Bayesian Decision Networks
Environmental management often requires making decisions despite system uncertainty. One such example is mudflat mediation in flood control reservoirs. Reservoir mudflats limit development of diverse fish assemblages due to the lack of structural habitat provided by plants. Seeding mudflats with agricultural plants may mimic floodplain wetlands once inundated and provide fish habitat and achieve habitat management objectives. However, planting success is uncertain because of unpredictable water level fluctuations that affect plant survival and growth. Decision support tools can account for uncertainty that influences decision outcomes and reduce the risk in reservoir mudflat planting decisions. We used Bayesian decision networks and sensitivity analyses to quantify uncertainty surrounding mudflat plantings as supplemental fish habitat in four northwest Mississippi reservoirs. When averaged across all uncertainty, planting was the optimal decision only in Enid Lake. Response profiles indicated planting decisions depended on elevation contours within Enid, Sardis, and Grenada reservoirs. No planting was optimal at all elevations for Arkabutla Lake. These results provide a quantified basis for establishing best management practices and identify key system states that influence decision outcomes. The process used in this study to evaluate planting decisions can be applied to any reservoir by modifying reservoir dependent inputs to evaluate planting decisions to provide supplemental fish habitat.
Retention and dimensional changes of evergreen brush piles within a flood control reservoir
Brush piles (i.e., trees and large woody debris) are often installed in reservoirs to supplement fish habitat. The retention and dimensional change of brush piles after installation is important information that can be used to maximize the effectiveness of this management action. We evaluated the retention and dimensional change of 70 eastern red cedar Juniperus virginiana and bald cypress Taxodium distichum brush piles in an embayment of a drawdown reservoir up to four annual cycles of submergence and exposure. We used satellite imagery to supplement our onsite measurements of retention. We also examined spatial patterns of brush pile retention and dimensional change. Brush piles were lost at 10% per year, and their volume was lost at 14% per year. We compared our rates of brush pile retention and dimensional change with those from a holdout data set of 50 brush piles. Estimates between data sets did not differ statistically. Spatial patterns of retention and dimensional change coincided with morphological features in our study area, suggesting that retention and dimensional change is influenced by variable physical forces (e.g., wave action and flow) at installation locations. Our estimates of brush pile retention and dimensional change can be used to generally sustain desirable brush densities. For example, to maintain a fixed total volume of brush in our study embayment, roughly 23% of the total brush volume installed would need to be replaced annually. Similar research in reservoirs managed for other purposes is needed, as length and cycle of inundation could lead to variable rates of retention and dimensional change. Additionally, advancements into computer-assisted detection and volume estimation could reduce the time and effort needed to monitor brush piles.
Fishing gear performance nearshore is substantiated by spatial analyses
We estimated whether the fish assemblages nearshore represented by electrofishing and gillnetting indexed location of reservoirs in a river basin. We expected that location in the basin would reflect a multiplicity of factors that determine fish habitat and fish assemblage composition, and therefore also anticipated a correlation between fish species composition and spatial variables if the gear type reflected legitimate differences in fish assemblages. We collected 1.6 million fish of 129 species in 22 reservoirs of the Tennessee River basin, USA. Standardized electrofishing represented different aspects of the fish assemblages than standardized gillnetting. Nevertheless, the assemblages documented by each gear type were correlated with the spatial location of the reservoirs in the river basin. Thus, even as these gear types reflected different aspects of existing fish assemblages, they each tracked spatial differences, suggesting that they reflected standing fish assemblages. Our study supports the use of standardized boat electrofishing and gillnetting as proper means for monitoring fish assemblages at large spatial scales. Our results further suggest that a well-designed and standardized sampling protocol can in fact provide an informative bird’s eye view of fish assemblages at regional, national, or continental scales suitable for informing conservation programs.
Selection of habitat-enhancing plants depends on predator-prey interactions
Shallow areas of drawdown reservoirs are often devoid of adequate fish habitat due to degradation associated with unnatural and relatively invariable cycles of exposure and flooding. One method of enhancing fish habitat in these areas is to sow exposed shorelines with agricultural plants to provide structure once flooded. It remains unclear if some plants may be more suitable than others to provide effective fish habitat. To determine the fish habitat potential of various crops, we performed a replicated tank experiment evaluating the selection of agricultural plants by prey and predator fishes with and without the presence of the other. We submerged diverse treatments of potted plants in outdoor mesocosms stocked with prey and/or predator fish and monitored selection of plant species, stem density, and stem height over 0.5-h trials. Prey fish selected the densest vegetation, and selection was accentuated when a predator was present. Predators selected the second highest stem density and were more active when prey were present. Prey schooling was increased by predation risk, suggesting that cover was insufficient to outweigh the advantages of increased group size. Our data indicate that the perception of cover quality is reciprocally context dependent on predator–prey interactions for both predator and prey. Applications of the two most selected plant treatments in this study could enhance structural habitat for both predator and prey fishes in reservoirs, adding to their already reliable functionality as supplemental forage crops for terrestrial wildlife.
Habitat associations of black basses in a reservoir system
The habitat associations of three species of black bass Micropterus spp. were examined in six habitat types (i.e., sediment, gravel, rock, riprap, brush, and aquatic plants) along a cascade of 10 reservoirs in the Tennessee River. We tested whether habitat selection differed among the three species and whether species’ co-occurrence depended on habitat type. We found that some species occurred in some habitats in proportion to habitat availability (some at higher frequencies and some at frequencies lower than availability) and that juveniles and adults exhibited similar occurrence patterns. Our habitat selection results largely corroborate previous descriptions of black bass habitat associations and generally track preference for lithic habitats, as reported in native streams. We expected the different black bass species to show negative co-occurrence to avoid competitive interactions. Nevertheless, we found that with few exceptions, adults co-occurred in habitats mostly as expected by chance and juveniles co-occurred more often than was expected by chance. Our findings imply that environmental filtering, rather than competitive interactions that dominate in natural environments, may be the dominant mechanism shaping black bass assemblages in reservoirs of the Tennessee River. The observed patterns of habitat selection and co-occurrence further suggest that the conservation and management of black bass assemblages in reservoirs can be supported through habitat management activities. Protecting and enhancing the remaining lithic habitat in the reservoirs as well as recovering habitat that is blanketed by sediment could provide desirable environments for all black bass species.