Watershed Center

Zebra mussels represent one of the most pervasive and expensive non-native species to be introduced into new aquatic ecosystems, negatively impacting human structures and infrastructure and acting as ecosystem engineers. Zebra mussels have demonstrated thermal plasticity, enabling expansion to semi-tropical aquatic systems including Texas ca. 2009. In this study we described spawning and population dynamics and water quality changes after colonization of two central Texas reservoirs, Lake Austin and Lady Bird Lake, ca. 2017. Veliger concentrations peaked in spring and early summer (Julian days 120–170) when water temperatures were between 20–25 °C. Adult population densities were initially highest nearest the busiest boat ramps and peaked in 2019–2020. Densities declined thereafter in the lower sections, but generally increased upriver in Lake Austin. However, the decline throughout Lady Bird Lake was three orders of magnitude from the peak. After colonization, chlorophyll a and suspended solid concentrations significantly declined, concomitant with significant changes in water total phosphorus concentrations; changes in different nitrogen-form concentrations were mixed. However, water quality changes were exacerbated by changing discharge volumes. Recent drought conditions and reduced discharges after 2021 have also resulted in elevated water temperatures, notably in Lady Bird Lake, that may have contributed to observed declines in adult zebra mussel densities nearshore. We hypothesize that other southern United States reservoirs should expect similar variations in population dynamics which will impact municipal, recreational, and water quality attributes. Preventing introductions remains essential as the species continues to rapidly spread to new regions.

With the increasing global concern over plastics' environmental and human health impacts, the urgency for effective regulatory measures is evident. The UN Environment Assembly's initiative to establish an international, legally binding instrument via the Intergovernmental Negotiating Committee (INC) on Plastic Pollution marks a significant step toward addressing this issue. However, the vast diversity of plastic types and their myriad applications present a complex challenge in pinpointing the most critical targets for regulation. This study builds on the existing body of literature to outline potential key criteria for identifying Polymers of Concern (PoC). We recommend a dual-focused definition of PoCs considering both (1) the type of the plastics and (2) their domain of applications based on the environmental and human health impacts throughout the polymer's life cycle. Recognizing the current gaps in our understanding of the full spectrum of plastics' impacts across their life cycles, we suggest adopting a precautionary approach that factors in the volume of plastics entering natural ecosystems alongside their life cycle impacts as reported in the literature. We then bring forward existing data on the assessment of some of the main polymer types and applications. We propose that policymakers examine a wide spectrum of strategies including not only bans and phaseouts but also economic incentives, innovation, and the redesign of plastic materials and products to mitigate the adverse impacts of PoCs. We further emphasize the importance of thoroughly assessing the feasibility, costs, and environmental, social and economic implications of alternative materials to avoid “regrettable substitution.” We conclude by identifying existing knowledge gaps and emphasizing the need for further research to refine the proposed criteria for identifying PoCs.

Abstract Dissolved organic carbon (DOC) is a key component of aquatic ecosystems with complex effects on ecosystem function. While long‐term increases in DOC termed “brownification” have received considerable attention, directional trends typically account for a minority of variance. DOC concentrations also fluctuate on seasonal to multiannual timescales, but the causes of such variations are less understood. We used a wavelet‐based approach to study timescale‐specific, spatially synchronous fluctuations in DOC across 49 lakes in the Adirondacks, New York, USA. DOC varies synchronously among lakes at within‐season, annual, and interannual timescales, but relationships with external drivers and internal processes indicated by lake chemistry differed across timescales. External drivers explained 78% of spatial DOC synchrony at the annual time scale. Beyond positive trends related to regional recovery from acidification, variability in DOC is a consequence of fluctuations at several timescales that are common among Adirondack lakes in precipitation, solar radiation, and internal chemical concentrations.

Abstract Projections of global sea level depend sensitively on whether Thwaites Glacier, Antarctica, will continue to lose ice rapidly. Prior studies have focused primarily on understanding the evolution of ice velocity and whether the reverse‐sloping bed at Thwaites Glacier could drive irreversible retreat. However, the overall ice flux to the ocean and the possibility of irreversible retreat depend not only on the ice speed but also on the width of the main ice trunk. Here, we complement prior work by focusing specifically on understanding whether the lateral boundaries of the main ice trunk, termed shear margins, might migrate over time. We hypothesize that the shear margins at Thwaites Glacier will migrate on a decadal timescale in response to continued ice thinning and surface steepening. We test this hypothesis by developing a depth‐averaged, thermomechanical free‐boundary model that captures the complex topography underneath the glacier and solves for both the ice velocity and for the position of the shear margins. We find that both shear margins are prone to migration in response to ice thinning with basal strength and surface slope steepening determining their relative motion. We construct four end‐member cases of basal strength that represent different physical properties governing friction at the glacier bed and present two cases of ice thinning to contrast the effects of surface steepening and ice thinning. We test our model by hindcasting historic data and discuss how data from ongoing field campaigns could further be used to test our model.

Abstract Tracking habitat use and dietary shifts in migratory species is vital to conservation and management. Yet, conventional animal tracking often precludes tracking small juveniles at critical life stages where recruitment bottlenecks often manifest. Stable isotope analysis (SIA) in consecutive laminae in eye lenses, a protein‐rich depositional tissue, has emerged as a promising tool in fishes to develop long‐term interpretive records of dietary histories using a single archival tissue. Currently, studies using fish eye lenses to study SIA in diets have primarily been conducted in marine environments using δ 13 C and δ 15 N to identify resource partitioning, ontogenetic shifts and lifelong trophic histories. To date, no studies have examined freshwater taxa nor used δ 34 S isotopes. We placed juvenile (Chinook Salmon) Oncorhynchus tshawytscha in experimental enclosures in three different freshwater habitats (hatchery, river and seasonal floodplain), each with isotopically distinct and well‐characterized food webs. This experimental approach allowed us to directly measure diets and quantify tissue turnover rates in eye lenses as well as the isotopic fractionation among fish tissues (fin and muscle tissue) in distinct habitat types using stable isotopes δ 13 C, δ 15 N and δ 34 S. Bulk eye‐lens stable isotope measurements were analysed for juvenile salmon lenses and were found to be consistent with the isotopic values of rearing habitats. Slight additional isotopic fractionation was only found in δ 13 C. We then successfully applied the method to a larger, reproductively mature adult salmon captured in freshwater and inferred juvenile habitat use. SIA in eye lenses using three dietary isotopes (δ 13 C, δ 15 N and δ 34 S) has significant potential for answering critical questions about migration, diet, foraging ecology and life history of migratory aquatic animals on Earth. Such information would have immediate application towards conservation management of diverse species and habitats at multiple scales.

Maintaining beneficial, native plant structure and diversity while reducing invasive, nuisance species dominance is an important management domain for natural resource managers. One such vegetation component in North American lakes and reservoirs is submerged aquatic vegetation—a valuable aquatic resource which serves as productive habitat for fish, aquatic macroinvertebrates, and other wildlife. Reservoirs in the southern parts of the United States have experienced varying aquatic plant dominance dynamics due to historical water resource management actions, including drawdowns and introduction of herbivorous fish for the purpose of controlling invasive aquatic vegetation. Some of these management options have also been detrimental to native submerged aquatic vegetation. This paper explores an adaptive management research effort by installing herbivore-protected, fenced-pen submerged aquatic vegetation sites in a high-herbivore reservoir to determine effectiveness of protecting habitat and serving as founder colony sources for propagule spread. Four experimental sites with three management treatments each were planted with American eelgrass. Each site utilized one un-fenced treatment and two treatments with varying mesh sizes for protective fencing-pens. Site integrity, species survival and spread, and grazing were documented. One additional site was installed and planted with other native submerged aquatic vegetation species for nominal species performance descriptions. No plants survived unprotected in the high-herbivore system and plants, in general, performed consistently better within the smaller mesh size. These test planting results were ultimately used to inform adaptive management decision making for plant installation and expansion designs for managing reservoirs invested with Hydrilla, considered one of the most serious invasive aquatic plants in the United States.

HighlightsNitrogen loss reduction due to a cover crop tends to improve with increased cover crop biomass production.Mixed phosphorus loss reduction results in cold climates where freeze-thaw cycles occur and can increase dissolved phosphorus losses.Cereal rye was the primary cover crop studied and tended to provide the most water quality benefits.Abstract. Mitigating nutrient losses from agricultural fields retains these nutrients for subsequent crop production and reduces the risk to downstream water quality. This study evaluated the impact of cover crops, as part of an annual cropping system, on reducing nutrient losses and enhancing water quality. Cover crop literature focusing on water quality was reviewed to determine important factors regarding cover crop performance and cost. Results show that a grass-based cover crop and mixes with grasses tend to increase nitrate loss reduction (40%) compared to legumes (negligible). Biomass growth was also important, with early seeding or growth of a cover crop in areas with increased growing degree days enhancing performance. For phosphorus loss, benefits did not necessarily increase with increasing biomass. Further, dissolved phosphorus concentrations may increase due to freeze-thaw cycles (23%), although overall dissolved phosphorus losses tend to decrease due to less runoff (34%). Cover crop implementation costs ranged from a savings of $25 to $44 ha-1 year-1 before soybeans and corn, respectively, when implementing a cover crop for five straight years to a cost of $193 ha-1 year-1. Including a cover crop in annual crop rotations with adequate time in the fall for germination and growth can reduce nitrogen and phosphorus losses from production agriculture to help meet water quality goals across the U.S. Keywords: Catch crop, Nitrogen, NRCS, Phosphorus, Practice Code 340, USDA, Water quality.

Augustina Kwesie Osabutey Environmental Engineering Department, Montana Technological University, Butte, MT.