Increased Water Clarity Research Articles

Multiple signs of ecosystem change in the zooplankton community of a large temperate lake

Large lakes, such as Lake Simcoe, Ontario, Canada, are undergoing significant change due to local and global stressors. Uni- and multivariate analyses of Lake Simcoe's zooplankton community from 1986 to 2012 indicated multiple events of ecosystem change that were synchronous across three lake stations . In the mid-1990s, shifts in zooplankton species abundance and richness, and total cladoceran body size were strongly correlated with the invasion of the zooplanktivore, Bythotrephes cederstroemii. In the early 2000s, additional shifts in zooplankton abundance, as well as copepod body size, coincided with increased water clarity (linked to filter feeding by the invader Dreissena polymorpha) and hypolimnetic water temperature. Further community changes occurred in the 2000s when Bythotrephes declined and many vulnerable cladoceran species recovered. However, the Lake Simcoe community did not fully return to its pre-invasion state as the cold-water herbivores, Daphnia longiremis and Daphnia pulicaria, remained absent. The Lake Simcoe zooplankton community illustrates ongoing ecosystem change that propagated throughout the lake food web and may be reflected in other lakes experiencing global stressors of climate change and species invasions.

Dry Me a River: Ecological Effects of Drought in the Upper San Francisco Estuary

Droughts have major effects on estuaries because freshwater entry is one of the defining features of an estuary, and freshwater flow is an important variable that determines the interannual change in the environment. In the upper San Francisco Estuary (the Sacramento–San Joaquin Delta, Suisun Bay, and Suisun Marsh), the Mediterranean climate includes frequent multi-year droughts. To assess ecosystem responses to droughts in the upper estuary, the Interagency Ecological Program Drought Synthesis Team assembled a set of flow, water quality, chlorophyll, zooplankton, and fish data from 1975 to 2021 to test for differences between multi-year droughts and multi-year wet periods and tested for linear relationships between each variable and the Sacramento Valley Hydrologic Index (see definitions and relationships as outlined in Appendix A). Our models showed droughts decreased Delta outflow, project exports, zooplankton in Suisun Bay, and some fish species. We also found that droughts increased water clarity, salinity, nutrients, chlorophyll in the South Delta, zooplankton in the South Delta, and water residence time. Although our analyses only tested correlations, we hypothesized that most of the food-web responses could be traced to increased residence time, decreased transport rates, or both. However, some responses may have been caused by secondary effects, including shifts in salinity gradients, regional changes in water quality, or differences in top-down effects of increased predation and grazing rates. With increased frequency of droughts in the future, this increasingly low-outflow, warming, clearing estuary—which is invaded by non-native species and has low pelagic fish production—is rapidly becoming the new “normal.”

Satellite imagery as a management tool for monitoring water clarity across freshwater ponds on Cape Cod, Massachusetts

Water clarity serves as both an indicator and a regulator of biological function in aquatic systems. Large-scale, consistent water clarity monitoring is needed for informed decision-making. Inland freshwater ponds and lakes across Cape Cod, a 100-km peninsula in Massachusetts, are of particular interest for water clarity monitoring. Secchi disk depth (SDD), a common measure of water clarity, has been measured intermittently for over 200 Cape Cod ponds since 2001. Field-measured SDD data were used to estimate SDD from satellite data, leveraging the NASA/USGS Landsat Program and Copernicus Sentinel-2 mission, spanning 1984 to 2022. Random forest machine learning models were generated to estimate SDD from satellite reflectance data and maximum pond depth. Spearman rank correlations (rs) were “strong” for Landsat 5 and 7 (rs = 0.78 and 0.79), and “very strong” for Landsat 8, 9, and Sentinel-2 (rs = 0.83, 0.86, and 0.80). Mean absolute error also indicated strong predictive capacity, ranging from 0.65 to 1.05 m, while average bias ranged from −0.20 to 0.06 m. Long- and recent short-term changes in satellite-estimated SDD were assessed for 193 ponds, selected based on surface area and the availability of maximum pond depth data. Long-term changes between 1984 and 2022 established a retrospective baseline using the Mann-Kendall test for trend and Theil-Sen slope. Generally, long-term water clarity improved across the Cape; 149 ponds indicated increasing water clarity, and 8 indicated deteriorating water clarity. Recent short-term changes between 2021 and 2022 identified ponds that may benefit from targeted management efforts using the Mann-Whitney U test. Between 2021 and 2022, 96 ponds indicated deteriorations in water clarity, and no ponds improved in water clarity. While the 193 ponds analyzed here constitute only one quarter of Cape Cod ponds, they represent 85% of its freshwater surface area, providing the most spatially and temporally comprehensive assessment of Cape Cod ponds to date. Efforts are focused on Cape Cod, but can be applied to other areas given the availability of local field data. This study defines a framework for monitoring and assessing change in satellite-estimated SDD, which is important for both local and regional management and resource prioritization.

Investigating the role of hydrological connectivity on the processing of organic carbon in tropical aquatic ecosystems

Inland waters are highways of carbon and nutrient flows between the land and ocean. Aquatic environments integrate multiple sources and processes over space and time that influence ecosystem functionality. The complexity of these systems and their multiple interactions with the surrounding environment are conceptualised, but often lack empirical scrutiny that allows further understanding of how inland waters mobilise, transport, and utilise carbon and nutrients. This is particularly evident in tropical waters. Here, we apply advanced geochemical analyses of dissolved organic matter (DOM) composition in conjunction with algal pigment biomarkers, to determine the seasonal variability of organic matter production, processing and export for a tropical, floodpulse wetland, Tasik Chini (Malaysia). We identify two phases in the hydrological cycle: Phase 1 signifying a transition from the wet season with high suspended sediment and dissolved organic carbon concentrations. DOM is composed of humic substances, building blocks and lower molecular weight compounds. Towards the end this phase then are periods of increased water clarity and algal productivity. This is followed by Phase 2, which has a greater contribution of autochthonous DOM, composed of proteinaceous material, concomitant with lower dissolved nutrient concentrations, increased mixotrophic algae and emergent vegetation. Based on this framework, we highlight the role of such tropical wetland lakes as hydrological “bottlenecks,” through a lentic/lotic switch that shifts aquatic transport of carbon and nutrients from lateral river continuum supply to flood pulses. We highlight the need to consider inherent biases of spatial and temporal scaling when examining freshwater ecosystems along the land-ocean aquatic continuum.

Impact of submerged macrophytes on growth and 2-MIB release risk of Pseudanabaena sp.: From field monitoringa to cultural experiments.

The off-flavor compound 2-methylisoborneol (2-MIB) is generally associated with the proliferation and metabolism of filamentous cyanobacteria in shallow freshwater ecosystems. Here field monitoring in East Taihu Lake from July to October 2021, along with cultural experiments, was conducted to determine the impact of submerged macrophytes on the growth and 2-MIB production of filamentous cyanobacteria. Pseudanabaena sp. was identified as the 2-MIB producer with the highest detection rate (100%) and correlation coefficient (R=0.68, p<0.001). The 2-MIB concentration and algal growth in the macrophyte-dominated zones were markedly decreased compared with those in the phytoplankton-dominated zone. Five submerged macrophytes classified into flat-leaf type (Vallisneria natans and Potamogeton crispus) and thin-leaf type (Hydrilla verticillata, Ceratophyllum demersum, and Myriophyllum spicatum) exhibited strong inhibition effects against Pseudanabaena sp.: Overall inhibition efficiencies (IEs) of 92.7%±6.8% and 92.7%±8.4% for cell growth and 2-MIB production were achieved, respectively. Moreover, the thin-leaf macrophytes exhibited significant higher IEs for cell growth (94.0% vs. 84.7%) and 2-MIB production (99.4% vs. 82.6%) than the flat-leaf macrophytes and can be selected as pioneer species in controlling odor problems. Nutrient uptake, increasing water clarity, shading effects, and allelopathic effects of the submerged macrophytes were found to be the dominant inhibition mechanisms.

Meta-analysis of ecosystem services associated with oyster restoration.

Restoration of foundation species promises to reverse environmental degradation and return lost ecosystem services, but a lack of standardized evaluation across projects limits understanding of recovery, especially in marine systems. Oyster reefs are restored to reverse massive global declines and reclaim valuable ecosystem services, but the success of these projects has not been systematically and comprehensively quantified. We synthesized data on ecosystem services associated with oyster restoration from 245 pairs of restored and degraded reefs and 136 pairs of restored and reference reefs across 3500km of U.S. Gulf of Mexico and Atlantic coastlines. On average, restoration was associated with a 21-fold increase in oyster production (mean log response ratio=3.08 [95% confidence interval: 2.58-3.58]), 34-97% enhancement of habitat provisioning (mean community abundance=0.51 [0.41-0.61], mean richness=0.29 [0.19-0.39], and mean biomass=0.69 [0.39-0.99]), 54% more nitrogen removal (mean=0.43 [0.13-0.73]), and 89-95% greater sediment nutrients (mean=0.67 [0.27-1.07]) and organic matter (mean=0.64 [0.44-0.84]) relative to degraded habitats. Moreover, restored reefs matched reference reefs for these ecosystem services. Our results support the continued and expanded use of oyster restoration to enhance ecosystem services of degraded coastal systems and match many functions provided by reference reefs.

Applying early warning indicators to predict critical transitions in a lake undergoing multiple changes.

Lakes are dynamic ecosystems that can transition among stable states. Since ecosystem-scale transitions can be detrimental and difficult to reverse, being able to predict impending critical transitions in state variables has become a major area of research. However, not all transitions are detrimental, and there is considerable interest in better evaluating the success of management interventions to support adaptive management strategies. Here, we retrospectively evaluated the agreement between time series statistics (i.e., standard deviation, autocorrelation, skewness, and kurtosis-also known as early warning indicators) and breakpoints in state variables in a lake (Lake Simcoe, Ontario, Canada) that has improved from a state of eutrophication. Long-term (1980 to 2019) monitoring data collected fortnightly throughout the ice-free season were used to evaluate historical changes in 15 state variables (e.g., dissolved organic carbon, phosphorus, chlorophyll a) and multivariate-derived time series at three monitoring stations (shallow, middepth, deep) in Lake Simcoe. Time series results from the two deep-water stations indicate that over this period Lake Simcoe transitioned from an algal-dominated state toward a state with increased water clarity (i.e., Secchi disk depth) and silica and lower nutrient and chlorophyll a concentrations, which coincided with both substantial management intervention and the establishment of invasive species (e.g., Dreissenid mussels). Consistent with improvement, Secchi depth at the deep-water stations demonstrated expected trends in statistical indicators prior to identified breakpoints, whereas total phosphorus and chlorophyll a revealed more nuanced patterns. Overall, state variables were largely found to yield inconsistent trends in statistical indicators, so many breakpoints were likely not reflective of traditional bifurcation critical transitions. Nevertheless, statistical indicators of state variable time series may be a valuable tool for the adaptive management and long-term monitoring of lake ecosystems, but we call for more research within the domain of early warning indicators to establish a better understanding of state variable behavior prior to lake changes.

Ecosystem-based fisheries management is attainable, affordable, and should be viewed as a long-term commitment: Experiences from Lake Vättern, Sweden

Lake Vättern is Sweden’s second largest lake and faces multiple environmental challenges such as climate change, pollutants and invasive alien species. Since its foundation in 1957, the Lake Vättern Society of Water Conservation (LVSWC) has been a local actor aiming to manage a broad range of environmental issues concerning the lake and its catchment. Stakeholders can be members of LVSWC, which also organises a fisheries co-management group mainly dealing with fisheries issues. Ecosystem-based fisheries management (EBFM) is a widely desired framework shaped to focus on ecosystems, involve stakeholders, and address environmental issues in an adaptive, integrated and holistic manner while also including societal aspects. We have investigated how the management of Lake Vättern relates to 15 central principles for EBFM. The study found that LVSWC and the fisheries co-management group work along and towards the EBFM principles in a locally adapted way. Several environmental improvements have been observed concurrently with LVSWC activity, such as increased water clarity, and a strengthened stock of the Arctic char (Salvelinus alpinus). Long-term commitment by European, national and regional authorities was seen as essential to maintain and improve EBFM functions for Lake Vättern, to ensure continuity in the work, rather than having to depend on short projects. Becasue literature examples of EBFM in lakes are scarce worldwide, this study provides a unique example of the pursuit of EBFM in lake ecosystem management.

Three-dimensional biogeochemical modeling of eutrophication in Edmonton stormwater ponds

A three-dimensional coupled hydrodynamic-biogeochemical model was applied to simulate and investigate causes of eutrophication in two stormwater ponds in the City of Edmonton (Alberta, Canada). The ponds differ in shape, surface area, depth and trophic state. Strong spatial gradients, in water column thermal structure and water quality state variables were observed (e.g., ∼10 °C; 0.1 mg L−1 PO4, 0.5 mg L−1 total P and 50 μg L−1 chlorophyll-a over ∼3m), showing the ponds were incompletely mixed systems. Using a single set of calibration parameters, which differed from calibrations to larger systems, the model accurately simulated these gradients, with errors being highest for NO3 and total chlorophyll-a (RMSE <64.3 μg L−1 and NRMSE<0.94. Simulation of total chlorophyll-a was at times visually inaccurate, particularly in the more eutrophic pond, but the normalized metrics (e.g., NRMSE) were consistent between ponds and with literature values. The model accurately predicted the trophic state (in more than 60% of the observations) and the distribution of phytoplankton community structure was simulated with marginal error (average ∼7%). Chlorophyll-a alone was not a suitable index to define trophic state in the ponds; suspended algae and macro-algae reduced pond aesthetics, while competing with phytoplankton for nutrients and was coincident with lower phytoplankton biomass and increased water clarity. Simulated remediation strategies, involving reduction of influent phosphorus and nitrogen fractions, showed that the trophic state of each pond could be improved from mesotrophic/eutrophic to oligotrophic/mesotrophic states by reducing nutrient loads at least 50%.

Effect of COVID-19 Anthropause on Water Clarity in the Belize Coastal Lagoon

The Coronavirus disease 2019 (COVID-19) pandemic halted human activities globally in multiple sectors including tourism. As a result, nations with heavy tourism, such as Belize, experienced improvements in water quality. Remote sensing technologies can detect impacts of “anthropauses” on coastal water quality. In this study, moderate resolution imaging spectroradiometer (MODIS) satellite data were employed along the Belizean coast to investigate impacts of the COVID-19 shutdown on water quality. The attenuation coefficient at 490 nm, Kd(490), was used as an indicator of water quality, with a lower Kd(490) indicating increased water clarity. Four Coastal Management Zones were characterized by marine traffic as high traffic areas (HTAs) and two as low traffic areas (LTAs). Monthly composites for two periods, 2002–2019 (baseline) and 2020 were examined for Kd(490). For months prior to the COVID-19 shutdown in Belize, there was generally no significant difference in Kd(490) (p &amp;gt; 0.05) between 2020 and baseline period in HTAs and LTAs. Through the shutdown, Kd was lower in 2020 at HTAs, but not for LTAs. At the LTAs, the Kd(490)s observed in 2020 were similar to previous years through October. In November, an unusually active hurricane season in 2020 was associated with decreased water clarity along the entire coast of Belize. This study provides proof of concept that satellite-based monitoring of water quality can complement in situ data and provide evidence of significant water quality improvements due to the COVID-19 shutdown, likely due to reduced marine traffic. However, these improvements were no longer observed following an active hurricane season.

Trends in submersed aquatic plant communities in a large, inland lake: impacts of an invasion by starry stonewort (Nitellopsis obtusa)

Ginn BK, Dias EFS, Fleischaker T. 2021. Trends in submersed aquatic plant communities in a large, inland lake: impacts of an invasion by starry stonewort (Nitellopsis obtusa). Lake Reserv Manage. 37:199–213. Aquatic plant and macroalgae (collectively, macrophyte) communities from Lake Simcoe (Ontario, Canada) were studied in lakewide, >200 site surveys in 2008, 2013, and 2018. Over this period, mean macrophyte biomass increased 5-fold, from 29.9 g (dry)/m2 in 2008 to 153.9 g (dry)/m2 in 2018, due to the arrival and expansion of invasive starry stonewort (Nitellopsis obtusa). First recorded in Lake Simcoe in 2009, starry stonewort has greatly altered the macrophyte community, particularly in shallow (<3 m) water where it outcompeted invasive Eurasian watermilfoil (Myriophyllum spicatum). By 2018, starry stonewort comprised 67.6% of the total macrophyte biomass in Lake Simcoe. In shallow, mesotrophic Cook’s Bay, comparison to studies from the 1980s shows an increased plant biomass due to increased water clarity, from phosphorus (P) abatement and invasive dreissenid mussels, with further increases after 2011 due to starry stonewort. Starry stonewort may continue to impact nearshore ecology, with shallow-water fish species losing habitat and refugia as the “forest-like” structure of the plant community is replaced by large, dense aggregations of starry stonewort. Recreational uses will also be impaired and landowner complaints of macrophyte wash-ups will increase, with municipalities and lake-based businesses bearing the cost of mitigation and control strategies. Future research should consider the impacts of starry stonewort to P cycling as, unlike aquatic plants that uptake sediment P, macroalgae use dissolved P as a nutrient source. A lack of communication and reporting on starry stonewort has enabled its spread through south-central Ontario and the Great Lakes Region. Moving forward, we need a better understanding of starry stonewort biology and need to develop effective control and management strategies.

Steady increase in water clarity in Jiaozhou Bay in the Yellow Sea from 2000 to 2018: Observations from MODIS

The Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance data were used to analyze the temporal and spatial distribution characteristics of water clarity (Zsd) in the Jiaozhou Bay, Qingdao, China, in the Yellow Sea from 2000 to 2018. Zsd retrieval models were regionally optimized using in-situ data with coincident MODIS images, and then were used to retrieve the Zsd products in Jiaozhou Bay from 2000–2018. The analysis of the Zsd results suggests that the spatial distribution of relative Zsd spatial characteristics in Jiaozhou Bay was stable, being higher Zsd in the southeast and a lower Zsd in the northwest. The annual mean Zsd in Jiaozhou Bay showed a significant upward trend, with an annual increase of approximately 0.02 m. Water depth and wind speed were important factors affecting the spatial distribution and annual variation of Zsd in Jiaozhou Bay, respectively.

The increasing water clarity of Tibetan lakes over last 20 years according to MODIS data

Water clarity is a comprehensive indicator of the water environment status. Studies have shown that in recent years the clarity of inland and ocean water has decreased in many parts of the world owing to the influence of climate change and human activities. However, changes in inland water clarity exclusively resulting from climate change are largely ignored because most inland water is being utilized by human beings for applications such as waterworks or aquaculture. Therefore, understanding the trends and reasons of inland water clarity under natural conditions is important to recognize the inland water environment shifts under the global changes. Because of the harsh environment, the lakes on the Tibetan Plateau are less disturbed by human activities and are ideal objects for studying water clarity variations attributed to climatic changes. Here, we describe water clarity changes as measured using the Secchi Depth (SD) in 152 big lakes with an area greater than 50 km2 based on in-situ investigations and the retrieval results from a high accuracy retrieval model (r = 0.94, P < 0.01). Most of the lakes had an SD of 3–10 m, although there was marked spatial variation and a significant positive correlation with lake area (P < 0.01). The mean SD of all 152 lakes significantly increased at a rate of 0.033 m/year (95% CI, 0.021–0.045; P < 0.01) between 2000 and 2019. Variations in lake SD were linked with temporal changes in precipitation, and related to spatial changes of water optical components including suspended matter (0.13 < R2 < 0.40, P < 0.01 or P < 0.05), fDOM (R2 = 0.24, P < 0.01) and chlorophyll-a concentration (R2 = 0.12, P < 0.01).The reconstructed lake water clarity in our study will improve the understanding of inland water clarity changes and provide basic data to study the heat exchanges between lake water and atmosphere.

Walleye inland lake habitat: considerations for successful natural recruitment and stocking in North Central North America

Raabe JK, VanDeHey JA, Zentner DL, Cross TK, Sass GG. 2019. Walleye inland lake habitat: considerations for successful natural recruitment and stocking in North Central North America. Lake Reserve Manage. 36:335–359. Walleye (Sander vitreus) occur naturally or through extensive introductions in many inland lakes (i.e., non-Laurentian Great Lakes) throughout North Central North America. Persistence of walleye in these systems is influenced by factors including habitat, species interactions, exploitation, and stocking. Managers have expressed concerns about recent declining walleye recruitment and abundance in many inland populations, despite various conservation efforts (e.g., stocking, regulations). Therefore, we synthesized the scientific literature to provide information on how habitat influences successful natural recruitment and stocking. Historical and more recent studies indicate walleye are most successful in coolwater, mesotrophic, intermediate-to-large (>100 ha) lakes and that they spawn close to shore, in shallow water, and predominately over gravel and cobble substrates. Recent studies suggest that age-0 recruitment bottlenecks are likely occurring between hatching and midsummer. Relatedly, survival of stocked walleye tends to be higher for large fingerlings over fry or small fingerlings. Modeling studies indicate walleye declines may be attributed to warmer water and increasing water clarity, especially in smaller lakes or those with higher Centrarchidae or northern pike (Esox lucius) abundance. Important future walleye research includes connecting spawning habitat quality and quantity with hatching and recruitment success and continued evaluation of influential factors in the first year and later life stages. Management should focus on identifying and protecting high quality lakes and important habitats (e.g., spawning), along with understanding habitat and biological factors to determine whether walleye populations can be improved (e.g., habitat projects, stocking, regulations) or in some cases not managed for altogether (e.g., too warm).

Plenty of room at the bottom: niche variation and segregation in large-bodied benthivores of boreal lakes

Realized trophic niches of aquatic consumers are expected to reflect the particular abiotic and biotic conditions of the ecosystems they occupy. We examined patterns in the position, size, and shape of trophic niches of two common benthivorous fishes, white sucker (Catostomus commersonii) and lake whitefish (Coregonus clupeaformis), across boreal lakes using a stable isotope approach. In sympatry, white sucker niche positions reflected greater benthic reliance (higher δ13C) and lower trophic elevation (lower δ15N) compared with lake whitefish, and white sucker niche sizes (dispersion in δ13C–δ15N space) were also larger. Niche sizes of both species increased with maximum depth of lakes. Separation of trophic niche positions of the two species increased with increasing water clarity, but their niche sizes did not increase with increasing separation in their niche positions. White sucker occupied a niche position with slightly greater pelagic reliance and trophic elevation and had smaller trophic niches in the absence than in the presence of lake whitefish. Trophic niches of these benthivores appear to be shaped by both environmental factors and interspecific interactions.

Mutual Facilitation Among Invading Nuttall's Waterweed and Quagga Mussels.

Nuttall’s waterweed (Elodea nuttallii) is the most abundant invasive aquatic plant species in several European countries. Elodea populations often follow a boom-bust cycle, but the causes and consequences of this dynamics are yet unknown. We hypothesize that both boom and bust periods can be affected by dreissenid mussel invasions. While mutual facilitations between these invaders could explain their rapid parallel expansion, subsequent competition for space might occur. To test this hypothesis, we use data on temporal changes in the water quality and the abundance of E. nuttallii and the quagga mussel Dreissena rostriformis bugensis in a temperate shallow lake. Lake Müggelsee (Germany) was turbid and devoid of submerged macrophytes for 20 years (1970–1989), but re-colonization with macrophytes started in 1990 upon reductions in nutrient loading. We mapped macrophyte abundance from 1999 and mussel abundance from 2011 onwards. E. nuttallii was first detected in 2011, spread rapidly, and was the most abundant macrophyte species by 2017. Native macrophyte species were not replaced, but spread more slowly, resulting in an overall increase in macrophyte coverage to 25% of the lake surface. The increased abundance of E. nuttallii was paralleled by increasing water clarity and decreasing total phosphorus concentrations in the water. These changes were attributed to a rapid invasion by quagga mussels in 2012. In 2017, they covered about one-third of the lake area, with mean abundances of 3,600 mussels m−2, filtering up to twice the lake’s volume every day. The increasing light availability in deeper littoral areas supported the rapid spread of waterweed, while in turn waterweed provided surface for mussel colonization. Quantities of dreissenid mussels and E. nuttallii measured at 24 locations were significantly correlated in 2016, and yearly means of E. nuttallii quantities increased with increasing mean dreissenid mussel quantities between 2011 and 2018. In 2018, both E. nuttallii and dreissenid abundances declined. These data imply that invasive waterweed and quagga mussels initially facilitated their establishment, supporting the invasional meltdown hypothesis, while subsequently competition for space may have occurred. Such temporal changes in invasive species interaction might contribute to the boom-bust dynamics that have been observed in Elodea populations.

Pool Chemical Injuries in Public and Residential Settings - United States, 2008-2017, and New York, 2018.

Pool chemicals are added to water in treated recreational water venues (e.g., pools, hot tubs/spas, and water playgrounds) primarily to protect public health. Pool chemicals inactivate pathogens (e.g., chlorine or bromine), optimize pH (e.g., muriatic acid), and increase water clarity, which helps prevent drowning by enabling detection of distressed swimmers underwater. However, pool chemicals can cause injuries if mishandled. To estimate the annual number of U.S. emergency department (ED) visits for pool chemical injuries, CDC analyzed 2008-2017 data from the National Electronic Injury Surveillance System (NEISS), operated by the U.S. Consumer Product Safety Commission (CPSC). During 2015-2017, pool chemical injuries led to an estimated 13,508 (95% confidence interval [CI]=9,087-17,929) U.S. ED visits; 36.4% (estimated 4,917 [95% CI=3,022-6,811]) of patients were aged <18 years. At least 56.3% (estimated 7,601 [95% CI=4,587-10,615]) of injuries occurred at a residence. Two thirds of the injuries occurred during the period from Memorial Day weekend through Labor Day. This report also describes a toxic chlorine gas incident that occurred at a public pool in New York in 2018. Pool chemical injuries are preventable. CDC's Model Aquatic Health Code (MAHC) is an important resource that operators of public treated recreational water venues (e.g., at hotels, apartment complexes, and waterparks) can use to prevent pool chemical injuries.

Water clarity and temperature effects on walleye safe harvest: an empirical test of the safe operating space concept

AbstractSuccessful management of natural resources requires local action that adapts to larger‐scale environmental changes in order to maintain populations within the safe operating space (SOS) of acceptable conditions. Here, we identify the boundaries of the SOS for a managed freshwater fishery in the first empirical test of the SOS concept applied to management of harvested resources. Walleye (Sander vitreus) are popular sport fish with declining populations in many North American lakes, and understanding the causes of and responding to these changes is a high priority for fisheries management. We evaluated the role of changing water clarity and temperature in the decline of a high‐profile walleye population in Mille Lacs, Minnesota, USA, and estimated safe harvest under changing conditions from 1987 to 2017. Thermal–optical habitat area (TOHA)—the proportion of lake area in which the optimal thermal and optical conditions for walleye overlap—was estimated using a thermodynamic simulation model of daily water temperatures and light conditions. We then used a SOS model to analyze how walleye carrying capacity and safe harvest relate to walleye thermal–optical habitat. Thermal–optical habitat area varied annually and declined over time due to increased water clarity, and maximum safe harvest estimated by the SOS model varied by nearly an order of magnitude. Maximum safe harvest levels of walleye declined with declining TOHA. Walleye harvest exceeded safe harvest estimated by the SOS model in 16 out of the 30 yr of our dataset, and walleye abundance declined following 14 of those years, suggesting that walleye harvest should be managed to accommodate changing habitat conditions. By quantifying harvest trade‐offs associated with loss of walleye habitat, this study provides a framework for managing walleye in the context of ecosystem change.

Feeding Access of Eastern Oysters to the Winter–Spring Phytoplankton Bloom: Evidence from Jamaica Bay, New York

The filtering capacity of dense bivalve populations can exert strong controls on phytoplankton biomass, leading to increased water clarity and reduced hypoxia. Bivalves, particularly oysters, therefore are the focus of many restoration efforts and ecosystem-based management plans. The hypothesis is tested that oysters have feeding access to the classic major phytoplankton bloom of the year in winter–spring. Jamaica Bay is a highly eutrophic urban estuary where oyster restoration is being considered as a means to improve water quality. Strong winter–spring and summer phytoplankton blooms occur in Jamaica Bay, and oyster feeding rates and oxygen consumption were examined to see if oysters would be able to feed during both seasonal pulses of phytoplankton. Temperature-related feeding rates were found to vary to the degree that feeding did not occur at the cold temperatures that exist during the winter–spring blooms. Indeed, feeding rate and proportion feeding were found to be zero at 10°C, which corresponds to March–April. But feeding would be vigorous in late spring and summer. Oysters, therefore, do not have the ability to regulate a major fraction of phytoplankton during the year in Jamaica Bay and likely in the rest of the mid-Atlantic states region and New England. Feeding rates are much higher during the time of the summer blooms, and oysters in shallow well-mixed waters would, therefore, have access to feeding and possibly control of phytoplankton biomass at this time.

Spatial distribution and filtering efficiency of Daphnia in a deep subtropical reservoir

Studies of Daphnia distribution and function could help people manage and protect water quality. We investigated how spatial distribution and filtering efficiency of Daphnia in the transition and lacustrine zones of the Nanwan Reservoir (China). Samplings were conducted seasonally for 2 years from six sites in the reservoir. Daphnia abundance and biomass were significantly higher in the lacustrine zone than in the transition zone. Similar composition and biomass of edible phytoplankton were found in the two zones, suggesting that food quantity could not explain high Daphnia distribution in the lacustrine zone. The variations of water velocity and food quality could help explaining Daphnia patchy distribution in the reservoir. On the one hand, rapid water velocity can cause the Daphnia decrement in the transition zone. On the other hand, the ratio of particulate organic carbon (POC) to chlorophyll-a (chl-a ) concentration was significantly higher in the transition zone, indicating more allochthonous material constituted the food source for Daphnia. The lower quality food likely suppressed Daphnia development in the transition zone. A linear regression between Daphnia abundance and Secchi depth (SD) may suggest a cause-effect relationship where increased filtering efficiency was responsible for increased water clarity to some extent.