Improve Water Clarity Research Articles

Exploring tourists’ preferences and willingness to pay for national park recreation improvements based on regret and utility comparison

Research on the improvement of national park recreation policies has attracted much attention to discrete choice experiments to obtain tourists’ preferences and willingness to pay. However, individual choice behavior is extremely complex, and the single Random Utility Maximization (RUM) model ignores anticipated regret and is insufficient to explain individuals’ actual choice behavior. To investigate whether regret influences tourists’ choices regarding the improvement of national park recreation attributes, this study introduces the Random Regret Minimization (RRM) model and explores the performance of polynomial logit models and hybrid latent class models in analyzing discrete choice models based on utility and regret. By constructing a hybrid utility-regret model, we examine how tourists trade off between attributes such as vegetation coverage, water clarity, amount of litter, and level of crowding in national park recreation. Results indicate that the RRM model has better goodness-of-fit and predictive ability than the RUM model, indicating that regret is a significant choice paradigm, and the hybrid model better explains respondents’ choices. Specifically, 62.5% of tourists’ choices are driven by regret, and regret-driven respondents are more inclined to increase vegetation coverage and improve water clarity, while utility-driven respondents are more inclined to reduce litter and crowding. This study not only provides a reference for managers to develop more optimal recreation improvement strategies but also offers theoretical insights for national park recreation improvement policies.

Assessment of raw and produced water quality at Al-Doura water treatment plant

Abstract The population growth rate has increased rapidly in recent years so there is an obligation to evaluate the productivity of produced water (PW) by investigating the operation of the Water treatment plant (WTP). WTP’s primary goal is to remove and destroy harmful organisms from contaminated water to make it safe for human consumption. The quality of PW depends on the performance of WTP. This study aims to assess the removal efficiency of Al-Doura WTP in Baghdad City/Iraq and ensure that the drinking water quality meets the drinking water standards. Twenty-two water quality parameters are analysed over four years (from January 2020 to December 2023). The samples of raw water are collected from the Tigris River at the intake of the WTP, while the PW samples are collected at the final stage where the water undergoes treatment before being distributed to the consumers through the network. The measured parameters are Temperature, Turbidity, Alkalinity as CaCO3, Total Hardness as CaCO3, Calcium as Ca, Chloride as Cl, Magnesium as Mg, pH, Colour, Electrical Conductivity EC, Free chlorine (Residual chlorine), Sulphate as SO4, Total dissolved solids, Suspended solids, Iron as Fe, Fluoride as F, Aluminium as AL, Nitrite as NO2, Nitrate as NO3, Ammonia as NH3, Silica as Sio2, and Orthophosphate as PO4. In this study, special focus is concerned with some of these water quality parameters, temperature, pH, electrical conductivity EC, and Turbidity. The analysis is sub-categorized into winter and summer seasons. The SPSS software is used to analyse the data. The results indicate that there is no significant difference between the temperature of raw water and that of the produced water, and the pH values indicate slight alkalinity for raw water in both seasons. Electrical conductivity Ec values for both raw and produced water are found always greater in winter than in summer. The turbidity is found to satisfy the permissible limits for both the Iraqi and World Health Organisation standards (Turbidity < 5 NTU). The drinking water produced from the Al-Doura water treatment plant is found to be within Iraqi and WHO standards, The high difference in turbidity concentration before and after treatment and the removal efficiency excellent value of close to 98% indicates that the plant is highly effective and reflects the effective process of Al-Doura WTP in removing particulate matter and improving water clarity. The Pearson, correlation analysis results indicate a strong (positive, and negative) correlation in the relationship among some parameters reported in this article.

Estimating biofilm activity on biofilter elements in recirculating aquaculture systems (RAS) for rearing Atlantic salmon parr (Salmo salar) during operation with ozone and peracetic acid

Chemical disinfection in a recirculating aquaculture system (RAS) may affect biofilm-associated bacteria and the nitrification performance in the biofilter units. The biofilm response to chemical disinfectants in RAS remains unclear, but it can be understood using methods to quantify biofilm activity. Here, we compared the effects of two disinfection strategies, continuous ozone at 0.06 mg/L Cl2 equivalent (Ozone group) and peracetic acid (PAA) at 1 mg/L (PAA group) to control group without disinfectant, on biofilm activity on biofilter elements from nine identical experimental RAS with Atlantic salmon parr (Salmo salar) during a four-week trial. Biofilm activities on biofilter elements from the three groups were examined by measuring oxygen consumption rates (OCR) following sequential spiking with pure tap water, and tap water spiked with nitrite or ammonium, as well as oxygen release rate (kor) following hydrogen peroxide (H2O2) addition, to estimate metabolic activities of biofilm related to endogenous respiration and substrate turnover. The results show that the applied PAA dose increased the endogenous respiration activity of biofilm by 39–133%, stimulated the rate of biofilm enzymatic decomposition of H2O2 by 135%, and partially impaired the biofilm metabolism for nitrite oxidation (decrease by 36%), resulting in a significant nitrite accumulation (rise by 59%) in the cultured water, compared to control over experimental period. Ozone treatment caused an enhanced endogenous respiration activity of biofilm at the beginning of the experiment (increase by 45–74%), but dropped to control levels at the end of the experiment. The results indicate that chronic exposure to PAA can alter the metabolic state of biofilm, which can have consequences for biofilter functions, while chronic exposure to ozone improved water clarity without compromising the metabolic status of biofilm. The investigations provided insights into biofilm response to chemical disinfectant in RAS, which would benefit the optimization of an effective and safe use of disinfectants in RAS.

Water quality in a shallow eutrophic lake is unaffected by extensive thinning of planktivorous and benthivorous fish species

Ambitious to fulfill the European Water Framework Directive obligations, the European governments support projects to rehabilitate lakes with poor water quality. However, most lake restorations having relied on biomanipulation by fish thinning have failed to improve or even maintain water quality. Previous attempts removed all target fish species simultaneously, thus making it impossible to assess the specific impact of each feeding group on water chemistry. Lake Bromme was selected for extensive, time-selective fish biomanipulation to improve water clarity and promote submerged macrophytes and piscivorous fish stocks over a three-year monitoring period. Thinning of adult benthivorous bream (Abramis brama) and tench (Tinca tinca) was conducted throughout year one while thinning in years two and three targeted planktivorous roach (Rutilus rutilus), juvenile bream, and small perch (Perca fluviatilis). Yearly fish surveys assessed changes in fish population structure and biomass. Water quality parameters were monitored continually, and the cover of submerged macrophytes was surveyed annually via sonar. We found no improvement in water clarity or reductions of nutrients, organic particles, chlorophyll concentrations, or watercolor, despite a 6-fold thinning of total estimated fish biomass, from 112 to 19 kg ha−1. Over the period, the macrophyte cover increased from 0.8 to 13.5 %, but no recruitment of large piscivorous fish (perch and pike (Esox lucius) > 10 cm) was detected. We found higher correlations of particle concentration and water clarity to water temperature than to wind speed, which indicates sediment particle resuspension by the remaining fish community (mostly carp Cyprinus carpio) that forage on benthos in shallow lakes. Further system-ecological research in Lake Bromme should evaluate whether thinning the stock of carp and increasing plant cover may improve water quality and test which optical properties sustain high water turbidity and prevent shallow, eutrophic lakes like Lake Bromme from responding to intense fish thinning.

Using benefit transfer to estimate housing value increases from improved water clarity: A case study of lakes in Kosciusko County, Indiana.

This study provides step-by-step guidance for practitioners and local stakeholders on how to use existing study results to conduct benefit transfer (BT), and ultimately make informed predictions of how improvements in lake water clarity may benefit surrounding communities. The procedures are demonstrated using a publicly available meta-dataset developed by the United States Environmental Protection Agency, and a subsequent meta-analysis that synthesizes the literature on how improvements in water clarity impact home values. The BT procedures are demonstrated using a case study of 14 large lakes in Kosciusko County, Indiana. Lake-specific average increases in home values, as well as the value of the housing stock in aggregate, are calculated for illustrative improvements in lake water clarity. This analysis provides a critical bridge to better connect high-quality, academic research with real-world policy analysis, and ultimately serves to better equip local governments and stakeholders to make more informed policy and land use decisions.

Water treatment: Aluminum sulfate, polymer, and activated carbon between efficacy and overdosing. Case of Oum Er-Rbia River, Morocco

This article examines the impact of aluminum sulfate, polymer, and activated carbon on water treatment processes. General observations indicate that aluminum sulfate effectively reduces turbidity, but excessive use can result in reagent wastage. Similarly, polymer addition reduces turbidity up to an optimal dosage, beyond which it may contribute to increased turbidity and the same thing for activated carbon. The study emphasizes the significance of conducting jar tests to optimize the quantities of these chemicals through design of experiments (DOE), aiming to improve treatment effectiveness in order to meet international requirements in term of turbidity norms while reducing costs. By achieving the right balance, water treatment processes can efficiently remove suspended solids, leading to improved water clarity.

Improvements in water clarity and submersed aquatic vegetation cover after exclusion of invasive common carp from a large freshwater coastal wetland, Delta Marsh, Manitoba

Once introduced to shallow aquatic ecosystems common carp (Cyprinus carpio) often degrade habitat, negatively impacting the native organisms that rely on these systems. Detrimental effects often observed following the introduction of carp include a reduction in water clarity as bottom sediments become disturbed and resuspended and phytoplankton blooms become more severe and frequent. This results in a reduction of submersed aquatic vegetation (SAV), the effects of which are felt across multiple trophic levels. We sought to limit large carp (>70 mm maximum body width) access to a culturally and biologically significant 18,500 ha freshwater coastal wetland located in Manitoba, Canada to restore pre-carp conditions which were characterized by clear water and abundant SAV. In winter 2012–2013, exclusion structures were built to limit access by large carp to Delta Marsh during the spring and summer. A monitoring program (2009–2018) compared marsh conditions before and after carp exclusion. Water clarity improved following carp exclusion, largely driven by a reduction of inorganic suspended solids (ISS) rather than phytoplankton biomass, indicating that maintaining clear water conditions might be supplemented by reductions in nutrient export from agricultural areas adjacent to the marsh. The decrease in ISS and phytoplankton varied spatially, with the greatest change observed in the westernmost area of the marsh which is more sheltered compared to the large open bays characterizing eastern areas of the marsh. SAV doubled in percent cover through the 6 years of monitoring post-carp exclusion and SAV cover and species richness in the marsh was comparable to what was present in the early 1970s when there was also partial carp exclusion. Similar to water clarity, the increase in SAV cover was most significant in sheltered areas of the marsh. Our results suggest that excluding large carp can improve water clarity, SAV cover, and SAV species richness in large freshwater wetlands, benefiting waterfowl and other species.

Making waves: Lessons learned from the COVID-19 anthropause in the Netherlands on urban aquatic ecosystem services provisioning and management

The anomalous past two years of the COVID-19 pandemic have been a test of human response to global crisis management as typical human activities were significantly altered. The COVID-instigated anthropause has illustrated the influence that humans and the biosphere have on each other, especially given the variety of national mobility interventions that have been implemented globally. These local COVID-19-era restrictions influenced human-ecosystem interactions through changes in accessibility of water systems and changes in ecosystem service demand. Four urban aquatic case studies in the Netherlands demonstrated shifts in human demand during the anthropause. For instance, reduced boat traffic in Amsterdam canals led to improved water clarity. In comparison, ongoing service exploitation from increased recreational fishing, use of bathing waters and national parks visitation are heightening concerns about potential ecosystem degradation. We distilled management lessons from both the case studies as well as from recent literature pertaining to ecological intactness and social relevance. Equally important to the lessons themselves, however, is the pace at which informed management practices are established after the pandemic ends, particularly as many communities currently recognize the importance of aquatic ecosystems and are amenable to their protection.

Towards climate-robust water quality management: Testing the efficacy of different eutrophication control measures during a heatwave in an urban canal

Harmful algal blooms are symptomatic of eutrophication and lead to deterioration of water quality and ecosystem services. Extreme climatic events could enhance eutrophication resulting in more severe nuisance algal blooms, while they also may hamper current restoration efforts aimed to reduce nutrient loads. Evaluation of restoration measures on their efficacy under climate change is essential for effective water management. We conducted a two-month mesocosm experiment in a hypertrophic urban canal focussing on the reduction of sediment phosphorus (P)-release. We tested the efficacy of four interventions, measuring phytoplankton biomass, nutrients in water and sediment. The measures included sediment dredging, water column aeration and application of P-sorbents (lanthanum-modified bentonite - Phoslock® and iron-lime sludge, a by-product from drinking water production). An extreme heatwave (with the highest daily maximum air temperature up to 40.7 °C) was recorded in the middle of our experiment. This extreme heatwave was used for the evaluation of heatwave-induced impacts. Dredging and lanthanum modified bentonite exhibited the largest efficacy in reducing phytoplankton and cyanobacteria biomass and improving water clarity, followed by iron-lime sludge, whereas aeration did not show an effect. The heatwave negatively impacted all four measures, with increased nutrient releases and consequently increased phytoplankton biomass and decreased water clarity compared to the pre-heatwave phase. We propose a conceptual model suggesting that the heatwave locks nutrients within the biological P loop, which is the exchange between labile P and organic P, while the P fraction in the chemical P loop will be decreased. As a consequence, the efficacy of chemical agents targeting P-reduction by chemical binding will be hampered by heatwaves. Our study indicates that current restoration measures might be challenged in a future with more frequent and intense heatwaves.

Appreciation of Nordic landscapes and how the bioeconomy might change that: Results from a discrete choice experiment

Surface waters and their catchments provide societal benefits through cultural ecosystem services like recreation and appreciation of nature. The supply of cultural services depends on landscape characteristics like the extent of forested area, water clarity and the intensity of land use. These attributes vary spatially and will likely be influenced by a possible transition to a bioeconomy, i.e. a shift towards more use of renewable, biological resources like forestry products. Using a discrete choice experiment, we quantified survey respondents’ preferences and willingness to pay for changing landscape attributes in six Nordic catchments and explored how different characteristics of both the landscape and respondents affect these preferences. Results from a mixed logit (MXL) model analysis show preference for a more equal distribution of agriculture and forest, improved water clarity, increased area used for nature reserves, reduced flood frequency and increased employment from agriculture, forestry and fishery. Variation in preferences between study areas is significant in several of these attributes, and likely linked to respondent characteristics. Since these attributes can be affected by the transition to a bioeconomy, policy makers should take into account the effects of this transition on the supply of cultural services by considering the effects on welfare generated by cultural services when implementing land management policy.

Particle capture by seagrass canopies under an oscillatory flow

Although seagrass canopies are known to enhance particle sedimentation, there is still limited knowledge about how seagrasses modify the vertical distribution of sediment particles; especially when particles come from allochthonous sources. This study determined the volume of particles trapped by the seagrass leaves, the amount that remains in suspension both within and above the canopy, and the amount deposited onto the seabed. A set of laboratory experiments were conducted in which hydrodynamic conditions and canopy densities were varied to mimic real field conditions. This study demonstrated and quantified previously recorded observations concerning the fate of sediment in seagrass meadows. Seagrass meadows decreased the amount of suspended sediment by capturing the sediment on the blades of the seagrass and by enhancing particle sedimentation on the seabed. However, particles trapped by the blades of seagrass in the whole canopy increased with canopy density and reduced the number of particles in suspension within the canopy. The ecological implications were significant, since a seabed covered by vegetation, when compared to a bare seabed, produced a reduction in the suspended sediment particles within the canopy, improving water clarity. Furthermore, canopies (compared to bare substrates) enhanced seabed sedimentation and the denser the canopy was, the greater the amount of sediment deposited on the seabed.

Effects of reduced shoreline erosion on Chesapeake Bay water clarity

Shoreline erosion supplies sediments to estuaries and coastal waters, influencing water clarity and primary production. Globally, shoreline erosion sediment inputs are changing with anthropogenic alteration of coastlines in populated regions. Chesapeake Bay, a prime example of such a system where shoreline erosion accounts for a large proportion of sediments entering the estuary, serves here as a case study for investigating the effects of changing sediment inputs on water clarity. Long-term increases in shoreline armoring have contributed to decreased erosional sediment inputs to the estuary, changing the composition of suspended particles in surface waters. This study examined the impact of shoreline erosion on water clarity using a coupled hydrodynamic-biogeochemical model. Experiments were conducted to simulate realistic shoreline conditions representative of the early 2000s, increased shoreline erosion, and highly armored shorelines. Together, reduced shoreline erosion and the corresponding reduced rates of resuspension result in decreased concentrations of inorganic particles, improving water clarity particularly in the lower Bay and in dry years where and when riverine sediment influence is low. This clarity improvement relaxed light limitation, which increased organic matter production. Differences between the two extreme experiments revealed that in the mid-estuary in February to April, surface inorganic suspended sediment concentrations decreased 3–7 mg L−1, while organic suspended solids increased 1–3 mg L−1. The resulting increase in the organic-to-inorganic ratio often had opposite effects on clarity according to different metrics, improving clarity in mid-Bay central channel waters in terms of light attenuation depth, but simultaneously degrading clarity in terms of Secchi depth because the resulting increase in organic suspended solids decreased the water's transparency. This incongruous water clarity effect, the spatial extent of which is defined here as an Organic Fog Zone, was present in February to April in all years studied, but occurred farther south in wet years.

Changes in aquatic vegetation communities based on satellite images before and after pen aquaculture removal in East Lake Taihu

为削减东太湖养殖污染，改善湖泊水质，苏州市于2018年底基本完成东太湖养殖围网拆除工作.围网拆除后，湖泊生态环境对此如何响应，已成为学者及相关管理部门关注的重点.水生植被在维持湖泊生态系统平衡、物质循环和净化水质方面发挥着重要的作用，是诊断湖泊生态系统健康状态的关键指标.本研究基于Sentinel-2卫星数据，利用分类决策树模型和基于生活史的沉水植被优势种群提取方法，监测了东太湖2017年（围网拆除前）和2019年（围网拆除后）的水生植被类群和沉水植被优势种群的空间分布.经验证，水生植被类群监测精度为82.66%，Kappa系数为0.77；沉水植被优势种群的监测精度为62.08%，Kappa系数为0.56.结果表明：围网拆除后，东太湖水生植被优势类群由围网拆除前的沉水植被转变为浮叶植被；沉水植被分布面积减少，且种群由优势度相差不大的七大优势种群逐步向菹草和伊乐藻占据绝对优势发展，逐渐趋于单一化.;To improve water quality and enhance ecological management, all the net-pen aquaculture facilities in the East Lake Taihu have been removed by the end of 2018. Understanding the impact of this activity on lake ecosystem health is critical to promote efficient ecological management. Aquatic vegetation, especially submerged aquatic vegetation is an essential component of healthy lake ecosystem, as they provide food and shelter, help to secure and stabilize shorelines and modulate nutrient circulation. Additionally, submerged aquatic vegetation can improve water clarity by competing for nutrient with algae. Monitoring submerged aquatic vegetation is fundamental to lake ecosystem health evaluation. In this study, we leverage Sentinel-2 data to map the temporal change of different types of aquatic vegetation types (i.e., emergent vegetation, floating-leaved vegetation and submerged aquatic vegetation), as well as the dominant submerged aquatic vegetation species. We found that the dominant vegetation shifted from submerged to floating-leaved vegetation after the pen aquaculture removal in East Lake Taihu. Meanwhile, the total coverage of submerged aquatic vegetation and its diversity significantly decreased, suggesting environmental degradation in this area. Our research indicated that removing net-pen culture has negative effect on lake ecosystem health. Efficient ecological management of this critical lake system requires comprehensive evaluation before they implement any management activities.

Interactive effects of bitterling fish and mussel on the community structures of plankton and benthic macroinvertebrates

放养河蚌，提高水体透明度以促进沉水植物生长，是湖泊生态修复中的常用手段之一.而小型杂食性鱼类鳑鲏依赖河蚌繁殖，河蚌放养可能会促进鳑鲏种群的发展；而鳑鲏与河蚌交互作用对水生态系统的影响仍研究较少.于2018年11—12月通过原位受控实验，设置对照组、河蚌组、鳑鲏组和河蚌+鳑鲏组，研究了鳑鲏（大鳍鱊Acheilognathus macropterus）与河蚌（背角无齿蚌Sinanodonta woodiana）对水质、浮游生物和底栖生物的影响.结果表明：鳑鲏显著增加了上覆水总氮、总磷、悬浮质和叶绿素a（Chl.a）浓度；但并未显著影响无机悬浮质的浓度，说明鳑鲏对沉积物的扰动作用较弱.此外，鳑鲏显著增加了浮游植物生物量和蓝藻的比例.浮游动物总生物量并未受鳑鲏的影响，但显著增加了浮游动物的丰度，其中以轮虫为主.鳑鲏组的底栖动物总丰度（主要为水丝蚓）显著高于对照组，说明鳑鲏对水丝蚓的摄食压力较低.鳑鲏与河蚌交互作用对总磷、Chl.a、浮游植物和浮游动物丰度具有显著影响：具体表现为河蚌虽然抵消了部分鳑鲏对水质（如氮、磷和悬浮质浓度，以及Chl.a浓度和浮游植物生物量等）的负面影响，但其对浮游动物和水丝蚓生物量的影响不显著.在湖泊生态修复和管理中，需要关注和重视鳑鲏等此类小型杂食性鱼类对水生态系统可能产生的负面影响，通过物理（网簖等）或生物（放养肉食性鱼类）等方式将其控制在较低密度水平，从而降低这些鱼类对水质、浮游生物和底栖生物群落可能产生的负面影响，维持生态修复效果的长效与稳定运行.;In restoration of shallow eutrophic lakes based on recovery of submerged macrophytes, stocking of the filter-feeding mussels has been commonly used for improving water clarity, thereby enhancing the growth of submerged macrophytes. However, the small omnivorous bitterling fish has to rely on mussels for breeding. Thus, the increased abundance of mussels may enhance the population development of bitterling. Nevertheless, the effects of bitterling (Acheilognathus macropterus) and their host mussels (Sinanodonta woodiana) on the aquatic ecosystems are, so far, not well-studied. We conducted a mesocosm experiment to study the effects of bitterling, mussels, and their interactions on water quality and the community structures of phytoplankton, zooplankton and benthic macroinvertebrates, respectively. Our results showed that bitterling did not substantially affect the concentration of inorganic suspended solids (ISS) indicating weak effects on sediment resuspension. However, the concentrations of total nitrogen and total phosphorus were significantly enhanced by bitterling. Consequently, both the abundance and biomass of phytoplankton were enhanced in the bitterling-only mesocosms, and cyanobacteria dominated the phytoplankton community at the end of the experiment. However, rotifers dominated the zooplankton community leading to a higher abundance of zooplankton in the bitterling-only treatment, while the total biomass of zooplankton did not differ significantly between the control and bitterling-only treatments. Moreover, bitterling significantly increased the total abundance of benthic macroinvertebrates compared with the controls, while the biomass of macroinvertebrates was not pronouncedly affected. The presence of mussels significantly eliminated the negative effects induced by bitterling, such as reducing the concentrations of nutrients, suspended solids and chlorophyll-a and phytoplankton biomass. However, the biomass of zooplankton and benthic macroinvertebrates were not substantially affected by the presence of mussels. Our results suggest that bitterling alone can induce significantly negative effects on water quality though mussels can eliminate part of these impacts under our experimental bitterling-to-mussel biomass ratio. Therefore, in the restoration and management of shallow lakes, more attention should be paid on the effects of small omnivorous fish, like bitterling, on aquatic ecosystems. The biomass of these small omnivores should be controlled at a relatively low level by physical (e.g., trap net) or biological (e.g., stocking of effective piscivorous fish) methods to minimize the negative effects of the fish on lake ecosystems.

Century-long records reveal shifting challenges to seagrass recovery.

Global losses over the 20th century placed seagrass ecosystems among the most threatened ecosystems in the world, with eutrophication, and associated deterioration of the submarine light environment identified as the main driver. Growing appreciation of the ecological and societal benefits of healthy seagrass meadows has stimulated efforts to protect and restore them, largely focused on reducing nutrient input to coastal waters. Here we analyze a unique data set spanning 135years on eelgrass (Zostera marina), the dominant seagrass of the northern hemisphere. We show that meadows in the Western Baltic Sea exhibited major declines relative to historic (1890-1910) reference due to the wasting disease in the 1930s followed by eutrophication peaking in the 1980s, but have only shown modest improvement despite major eutrophication mitigation, halving nitrogen input since the 1980s. Across the past century, we identified generally shallower colonization depths of eelgrass for a given submarine light penetration and, hence, increased apparent light requirements. This suggests that eelgrass recovery is limited by additional stressors. Our study indicates that bottom trawling and intense recent warming (0.5°C per decade, 1985-2018), which impact on deeper and shallower meadows, respectively, suppress eelgrass from fully recovering from eutrophication. Warming is most severe in shallow turbid waters, while clear-water areas offer eelgrass refugia from warming in deeper, cooler waters; but trawling can prevent eelgrass from reaching these refugia. Efforts to reduce nutrient input and thereby improve water clarity have been instrumental in avoiding a catastrophic loss of eelgrass ecosystems. However, local-scale future management must, in addition, reduce bottom trawling to facilitate eelgrass reaching deeper, cooler refugia, and increase resilience toward realized and further warming. Warming needs to be limited by meeting global climate change mitigation goals.

Effects of Diversity, Coverage and Biomass of Submerged Macrophytes on Nutrient Concentrations, Water Clarity and Phytoplankton Biomass in Two Restored Shallow Lakes

Transplantation of submerged macrophytes to restore shallow lakes has been used as an effective measure to maintain a clear water state. Water quality is highly correlated with submerged macrophytes community, however, the relationships between water quality and the diversity, coverage and biomass of submerged macrophytes are, so far, not yet well studied. We analyzed the correlations of nutrient concentrations, water clarity and phytoplankton biomass with the metrics of submerged macrophytes community in two Chinese restored shallow subtropical lakes, Lake Wuli (Wuli-E, 5 ha) and Lake Qinhu (Qin-E, 8 ha). A similar biomass of submerged macrophytes was transplanted into each lake, while both the species richness and coverage of macrophytes in Qin-E were lower than Wuli-E. After a 1–2-year restoration, the diversity almost had no change, but the biomass density and coverage decreased in Wuli-E. As for Qin-E, the coverage of submerged macrophytes increased but biomass density and diversity decreased. The dominance of canopy-forming submerged macrophyte species Myriophyllum spicatum was observed in Qin-E and less meadow-forming biomass and species was observed than that in Wuli-E. Moreover, it was also observed that Wuli-E had a better water quality than that of Qin-E after transplantation. Path analysis results showed that macrophyte coverage and the diversity related to meadow-forming species (e.g., Vallisneria spinulosa) had strong effects on enhancing clarity and reducing nutrient concentrations. But the high biomass density accompanied by the canopy-forming species like M. spicatum was unfavorable for controlling nutrients. Our results provide important insight into the different roles that macrophyte diversity, biomass and coverage play in improving water clarity and controlling nutrient concentrations. This new knowledge will be instrumental in implementing more effective lake restoration, especially using macrophyte transplantation as a restoration tool in warm shallow lakes.

Turbulence and Particle Deposition Under Steady Flow Along a Submerged Seagrass Meadow

AbstractSeagrass meadows can retain fine particles, improving water clarity and promoting carbon sequestration. Laboratory experiments were conducted to investigate the influence of velocity and meadow density on the retention of fine particles within a meadow. Vertical profiles of velocity and turbulent kinetic energy (TKE) were measured along a model meadow. The net deposition was measured using microscope slides positioned inside and outside the meadow. The deposition was correlated with the evolution of velocity along the meadow. At the leading edge, the net deposition decreased over a distance Lr, relative to the bare bed, which was associated with a region of vertical updraft and elevated TKE. Net deposition increased with the distance from the leading edge, associated with a decrease in vertical velocity and TKE. In some cases, a distinct peak in the deposition was observed at distance Lp from the leading edge, associated with a minimum in TKE. Both Lr and Lp decreased with increasing meadow density. Deposition in the fully developed region of the meadow decreased with decreasing stem density and increasing channel velocity, and for the lowest stem density and highest channel velocity the deposition in the meadow was less than that in the bare channel. Diminished deposition was linked to resuspension driven by stem‐generated turbulence. A model for canopy‐averaged TKE was validated and used to explore the range of field conditions for which TKE within a meadow would be reduced, relative to the bare bed, which would support the accumulation of fine organic material within the meadow.

How many submerged macrophyte species are needed to improve water clarity and quality in Yangtze floodplain lakes?

Successful re-establishment and maintenance of submerged macrophytes is a pivotal problem for the restoration of shallow eutrophic lakes, since submerged macrophytes can facilitate a shift of lake ecosystems from a turbid water state to a clear water state through their structuring roles. However, little is known about the optimal number of macrophyte species (species richness) needed for the recovery of shallow eutrophic lakes. Here, we investigated 19 shallow eutrophic lakes along the mid-lower reaches of the Yangtze River to reveal the underlying interrelations among water clarity, water quality and species richness. Our results showed positive correlations of water nutrients (TN and TP) with Kd and Red/Blue light ratio, suggesting that bad water quality can significantly lower water clarity. The results of path analysis indicated that the underwater light climate directly affects morphological and physiological traits and species richness of submerged macrophytes. Changes in functional traits also affected significantly the species richness of submerged macrophytes. Moreover, the presence of submerged macrophytes not only had positive effects on the underwater light climate (water clarity), but also on water quality. Most importantly, the assemblage of three or more submerged macrophyte species can significantly improve water clarity in these sampled eutrophic lakes, but not water quality. Additionally, the basic species assemblage of Myriophyllum spicatum and Vallisneria natans can be used for restoration of submerged macrophytes in shallow eutrophic Yangtze floodplain lakes. It is concluded that species richness and species assemblage are critical for recovery of submerged macrophytes in shallow eutrophic lakes.

Predicting the effects of eutrophication mitigation on predatory fish biomass and the value of recreational fisheries

Improving water clarity is a core objective for eutrophication management in the Baltic Sea, but may influence fisheries via effects on fish habitat suitability. We apply an ensemble of species distribution models coupled with habitat productivity functions and willingness-to-pay estimates to assess these effects for two coastal predatory fish species, European perch (Perca fluviatilis) and pikeperch (Sander lucioperca). The models predicted a 37% increase in perch and 59% decrease in pikeperch biomass if reaching the reference level for water clarity in the Baltic Sea Action Plan. Reaching the target level was predicted to increase perch biomass by 13%. However, the associated economic gain for the recreational fisheries sector was countervailed by an 18% pikeperch reduction. Still, a net benefit was predicted since there are six times more fishing days for perch than pikeperch. We exemplify how ecological modelling can be combined with economic analyses to map and evaluate management alternatives.

Regional trends in remotely sensed water clarity over 18 years in the Rotorua Lakes, New Zealand

ABSTRACTObservations by satellite sensors provide data on inland water systems at spatial and temporal coverage superior to current monitoring programmes. We derived an empirical relationship for Secchi depth using in situ data from eight lakes and data from the Landsat 5 Thematic Mapper, Landsat 7 Enhanced Thematic Mapper Plus and Landsat 8 Operational Land Imager between 1999 and 2018 in the Rotorua Lakes Region in New Zealand. This relationship was then applied to all Landsat data of 23 lakes in that region. A trend analysis on annual and summertime averages of Secchi depth revealed several statistically significant and positive trends, indicating improving water clarity. Our trends were in agreement with those based on in situ observations illustrating the opportunities of remote sensing time series data for lake monitoring and management.