Implications For Lake Management Research Articles

Water depth affects submersed macrophyte more than herbivorous snail in mesotrophic lakes.

Water depth (WD) and snail abundance (SA) are two key factors affecting the growth of submersed aquatic plants in freshwater lake ecosystems. Changes in WD and SA drive changes in nutrients and other primary producers that may have direct or indirect effects on submersed plant growth, but which factor dominates the impact of both on aquatic plants has not been fully studied. To investigate the dominant factors that influence aquatic plant growth in plateau lakes, a one-year field study was conducted to study the growth of three dominant submersed macrophyte (i.e., Vallisneria natans, Potamogeton maackianus, and Potamogeton lucens) in Erhai Lake. The results show that, the biomass of the three dominant plants, P.maackianus, is the highest, followed by P.lucens, and V.natans is the lowest. Meanwhile, periphyton and snails attached to P.maackianus are also the highest. Furthermore, WD had a positive effect on the biomass of two submersed macrophyte species of canopy-type P.maackianus and P.lucens, while it had a negative effect on rosette-type V.natans. Snail directly inhibited periphyton attached on V.natans and thereby increasing the biomass of aquatic plants, but the effect of snails on the biomass of the other two aquatic plants is not through inhibition of periphyton attached to their plants. The dominant factors affecting the biomass of submersed macrophyte in Erhai Lake were determined, as well as the direct and indirect mechanisms of WD and snails on the biomass of dominant submersed macrophyte. Understanding the mechanisms that dominate aquatic plant change will have implications for lake management and restoration.

Phosphorus accumulation during the ice-on season in macrophyte-dominated eutrophic lakes and its implications

Macrophyte overgrowth in eutrophic lakes can hasten the decline of shallow water bodies, yet the impact of macrophyte deposition on sediment phosphorus (P) accumulation in the ice-on season remains unclear. Comparative analyses of P variations among 13 semi-connected sub-lakes in Wuliangsu Lake in China, a typical MDE lake, considered external flow and macrophyte decomposition as driving forces. Sediment P fractions and water total phosphorus (TP) were analyzed at 35 sampling points across three ice-on season stages, along with macrophyte TP content to assess debris contributions.Our findings reveal that phosphorus accumulation occurs during the ice-on season in the MDE lake, with an average TP content increase of 16 mg/kg. However, we observed a surprisingly small sediment nutrient accumulation ratio (ΔTP/ΔTN=0.006) compared to macrophyte nutrient levels before decomposition. Further analysis of the dominant species, Potamogeton pectinatus, indicates that a significant portion (55%) of macrophyte phosphorus is released before the ice-on season. This highlights the critical importance of timing macrophyte harvesting to precede the phosphorus leaching process, which has implications for lake management and ecosystem restoration efforts.Additionally, our research demonstrates similar transformations among different sediment fractions as previously reported. Macrophyte debris decomposition likely serves as the primary source of Residual P (Res-P) or TP accumulation. In addition, Ca-bound P (Ca–P) generally showed a decrease, which mainly caused by its transformation to Fe/Al-bound P (Fe/Al–P), Exchange-P (Ex-P), and sometimes to Res-P. However, we emphasize the significant impacts of flow dynamics on Ca–P transport and transformations. Its hydrodynamic action increases water dissolved oxygen, which accelerates the transformation of Ca–P to more easily released Fe/Al–P and Ex-P. Furthermore, hydrodynamic transport also leads to upstream Ca–P transport to downstream. This underscores the necessity of considering flow dynamics when estimating phosphorus variations and formulating phosphorus restoration strategies.

Water Level Fluctuation Rather than Eutrophication Induced the Extinction of Submerged Plants in Guizhou’s Caohai Lake: Implications for Lake Management

The intensifying global decline in submerged aquatic lake plants is commonly attributed to lake eutrophication, while other drivers such as water levels are seldom considered. This study focused on the sudden extinction of the submerged plants in Caohai Lake, Guizhou, and employed long-term data and a whole-lake water level manipulation experiment to explore the impacts of nutrients and water level changes on the decline in submerged plants. The results indicated that over the past 40 years, the total nitrogen and ammonia nitrogen in the water did not change significantly, while the total phosphorus showed a significant decreasing trend. In recent years, however, the water level rose. The biomass of submerged plants continuously increased until a sudden large-scale extinction occurred in 2021; chlorophyll a also significantly increased. It is speculated that the large-scale extinction of the submerged plants was caused by water level fluctuations rather than eutrophication. After the restoration of the natural hydrological regime of low water levels in winter and spring and high levels in summer and autumn, the submerged plants gradually recovered, with the biomass increasing to 922.6 g/m2 in 2023. The structural equation modeling indicated that the water depth and bottom light availability were the main drivers for the changes in the submerged plants. However, in lake protection and management, more attention is often paid to controlling nutrients, while other influencing factors are neglected. These findings confirm the importance of water levels in the decline in and restoration of submerged plants in shallow lakes, suggesting a focus on water level management in lake protection and aquatic vegetation restoration.

Effect of Dam Emplacement and Water Level Changes on Sublacustrine Geomorphology and Recent Sedimentation in Jackson Lake, Grand Teton National Park (Wyoming, United States)

Dam installation on a deep hydrologically open lake provides the experimental framework necessary to study the influence of outlet engineering and changing base levels on limnogeological processes. Here, high-resolution seismic reflection profiles, sediment cores, and historical water level elevation datasets were employed to assess the recent depositional history of Jackson Lake, a dammed glacial lake located adjacent to the Teton fault in western Wyoming (USA). Prograding clinoforms imaged in the shallow stratigraphy indicate a recent lake-wide episode of delta abandonment. Submerged ∼11–12 m below the lake surface, these Gilbert-type paleo-deltas represent extensive submerged coarse-grained deposits along the axial and lateral margins of Jackson Lake that resulted from shoreline transgression following dam construction in the early 20th century. Other paleo-lake margin environments, including delta plain, shoreline, and glacial (drumlins, moraines) landforms were likewise inundated following dam installation, and now form prominent features on the lake floor. In deepwater, a detailed chronology was established using137Cs,210Pb, and reservoir-corrected14C for a sediment core that spans ∼1654–2019 Common Era (CE). Dam emplacement (1908–1916 CE) correlates with a nearly five-fold acceleration in accumulation rates and a depositional shift towards carbonaceous sediments. Interbedded organic-rich black diatomaceous oozes and tan silts track changes in reservoir water level elevation, which oscillated in response to regional climate and downstream water needs between 1908 and 2019 CE. Chemostratigraphic patterns of carbon, phosphorus, and sulfur are consistent with a change in nutrient status and productivity, controlled initially by transgression-driven flooding of supralittoral soils and vegetation, and subsequently with water level changes. A thin gravity flow deposit punctuates the deepwater strata and provides a benchmark for turbidite characterization driven by hydroclimate change. Because the Teton fault is a major seismic hazard, end-member characterization of turbidites is a critical first step for accurate discrimination of mass transport deposits controlled by earthquakes in more ancient Jackson Lake strata. Results from this study illustrate the influence of dam installation on sublacustrine geomorphology and sedimentation, which has implications for lake management and ecosystem services. Further, this study demonstrates that Jackson Lake contains an expanded, untapped sedimentary archive recording environmental changes in the American West.

Editorial: The effects of benthic-pelagic coupling on shallow lake ecosystems: Implications for lake management

Editorial: The effects of benthic-pelagic coupling on shallow lake ecosystems: Implications for lake management

Determining heavy metal pollution in sediments from the largest impounded lake in the eastern route of China's South-to-North Water Diversion Project: Ecological risks, sources, and implications for lake management

The eastern route of the South-to-North Water Diversion Project (ER-SNWDP) is a major human health project designed to alleviate the water scarcity in the Beijing-Tianjin-Hebei region in China. Impounded lake water security is directly related to the water diversion project effectiveness. At present, there is not a thorough understanding of the sediment heavy metals in Lake Hongze, the largest impounded lake of the ER-SNWDP. Consequently, this study reports a distribution analysis of Cu, Zn, Pb, Cr, Cd, As, Hg, and Ni in 101 sediment samples from Lake Hongze; we, utilized the enrichment factor, geoaccumulation index, and potential ecological risk index for the are to determine the ecological risk of heavy metals. The heavy metal source was examined with correlation analysis and principal component analysis–multiple linear regressions. The results showed that the average heavy metal content (Cu, Zn, Pb, Cr, Cd, As, Hg, Ni) were 0.03–1.57 times greater than the Jiangsu Province background values. Cd, As, and Hg were the main contributors to the Lake Hongze ecological risk. Spatially, the open water area was the most polluted among the four lake parts, and most of the flushing area had a low ecological risk. Chengzi bay and the western lake area have similar risk profiles, but are lower than the open water area risk. Source analysis showed that nonpoint-source agricultural pollution and industrial production were important pollution sources, while a considerable portion of the heavy metal content came from atmospheric deposition and natural sources. This study identified the main contamination areas and revealed the possible sources of each heavy metal; as such, this study can serve as a reference for the remediation and management of Lake Hongze to ensure the water safety of the ER-SNWDP.

Phytoplankton Composition and Their Related Factors in Five Different Lakes in China: Implications for Lake Management.

In this paper, two trophic lakes: Lake Taihu and Lake Yanghe, and three alpine lakes: Lake Qinghai, Lake Keluke, and Lake Tuosu, were investigated to discover the connections between environmental factors and the phytoplankton community in lakes with differences in trophic levels and climatic conditions. Three seasonal data, including water quality and phytoplankton, were collected from the five lakes. The results demonstrated clear differences in water parameters and phytoplankton compositions in different lakes. The phytoplankton was dominated by Bacillariophyta, followed by Cyanobacteria and Chlorophyta in Lake Qinghai, Lake Keluke, and Lake Tuosu. It was dominated by Cyanobacteria (followed by Chlorophyta and Bacillariophyta in Lake Yanghe) and Cyanobacteria (followed by Chlorophyta and Cryptophyta in Lake Taihu). The temperature was an essential factor favoring the growth of Cyanobacteria, Chlorophyta, and Bacillariophyta, especially Cyanobacteria and Chlorophyta. The pH had significantly negative relationships with Cyanobacteria, Chlorophyta, and Bacillariophyta. Particularly, a high pH might be a strong and negative factor for phytoplankton growth in alpine lakes. A high salinity was also an adverse factor for phytoplankton. Those results could provide fundamental information about the phytoplankton community and their correlated factors in the alpine lakes of the Tibetan Plateau, contributing to the protection and management of alpine lakes.

Determining Heavy Metal Pollution in Sediments of the Largest Impounded Lake of the Eastern Route of China's South-to-North Water Diversion Project: Ecological Risk, Sources, and Implications for Lake Management

Determining Heavy Metal Pollution in Sediments of the Largest Impounded Lake of the Eastern Route of China's South-to-North Water Diversion Project: Ecological Risk, Sources, and Implications for Lake Management

Nutrients and organic matter in the surface sediment of a submerged macrophyte zone in a eutrophic lake: Implications for lake management

Little is known about the distribution and risk levels of nutrients and organic matter (OM) in the surface sediment of shallow submerged macrophyte-dominated lakes. In the current study, sixty surface sediment samples were collected from Xukou Bay, a typical submerged macrophyte-dominated zone in Lake Taihu, China. A 60-day degradation experiment of Potamogeton malaianus, a dominant species in the bay, was done in the laboratory. The results demonstrated that the ranges of total nitrogen (TN) and total phosphorus (TP), alkali-hydrolyzable nitrogen (AN), available phosphorus (AP), and OM in the surface sediment of the bay were 262.2–2,979.6 mg/kg, 41.2–728.7 mg/kg, 8.6–150.0 mg/kg, 4.4–36.4 mg/kg, and 3.7–50.2 g/kg, respectively. The spatial distributions of TN, OM, and AN concentrations showed similar trends: The highest concentrations were present in the northeastern and southwestern zones, while the TP and AP concentrations were high in the northeastern, central, and southwestern zones. The heterogeneity in the spatial distribution of nutrients and OM in the surface sediment of the bay was associated with aquatic vegetation and anthropogenic activities. The comprehensive risk index and organic nitrogen index revealed that the surface sediment was moderately, interactively contaminated by TN and TP and by organic nitrogen. TN and OM in the northeastern zone were mainly derived from endogenous residues due to the decomposition of aquatic plants, while TN in the southwestern zone was primarily derived from agricultural wastewater. Consequently, targeted measures should be implemented to reduce TN and OM in the surface sediment of macrophyte-dominated lakes.

Density-dependent effects of omnivorous bitterling (Acheilognathus macropterus) on nutrient and plankton communities: implications for lake management and restoration

Shallow lakes are dominated by small omnivorous fish, but the roles of these small fish in aquatic ecosystems are not well-known. A small omnivorous bitterling (Acheilognathus macropterus) has been found to be dominant after lake restoration in shallow lakes. We conducted a mesocosm experiment to examine the effects of bitterling on water quality and plankton communities. Bitterling significantly increased the concentrations of nutrients, chlorophyll a (Chla) and suspended solids (TSS), and decreased the light intensity. The abundance and biomass of phytoplankton in the fish-present treatment were significantly higher than the controls, with Microcystis spp. and Dolichospermum spp. dominating the phytoplankton community. However, bitterling did not significantly affect the abundance and biomass of zooplankton, although the presence of bitterling shifted the community structure to dominance by small-sized species. Density-dependent effects of bitterling were observed on the concentrations of nutrient, TSS, organic suspended solids and Chla and on light intensity, but were not found for plankton and ratio of zooplankton to phytoplankton biomass. Our study indicates that A. macropterus can negatively affect water quality and facilitate the dominance of cyanobacteria. Therefore, monitoring and control of these small omnivorous species should be emphasized when restoring or managing shallow lakes.

Advancing aquatic vegetation management for fish in north temperate lakes

Radomski P, Carlson K, Perleberg D. 2019. Advancing aquatic vegetation management for fish in north temperate lakes. Lake Reserv Manage. 35:355–363.Despite the known linkage between aquatic plants and fish communities, research that quantifies the relationship between aquatic habitat and fisheries management is lacking, particularly for lakes. Lake management is often driven by recreational interests and fails to evaluate outcomes or identify conservation benefits. Effective management of vegetation to benefit fisheries will require information on how fish utilize aquatic plant stands, as well as how they are affected by changes in vegetation coverage or richness. Management strategies will need to account for both local and large-scale effects on aquatic plant habitat. Studies that assess the economic benefits of aquatic plants to fisheries will provide support for sustainable aquatic vegetation management approaches. Finally, natural resources managers (including both aquatic botanists and fisheries biologists) will have to collaborate to identify priorities to implement and evaluate vegetation management activities. Marine seagrass and fisheries research is presented as a means to provide guidance on aquatic plant inventory and monitoring, as well as potential research opportunities to better understand aquatic plant and fish relationships and the implications for lake management.

Fish-mediated plankton responses to increased temperature in subtropical aquatic mesocosm ecosystems: Implications for lake management

Although it is well established that climate warming can reinforce eutrophication in shallow lakes by altering top-down and bottom-up processes in the food web and biogeochemical cycling, recent studies in temperate zones have also shown that adverse effects of rising temperature are diminished in fishless systems. Whereas the removal of zooplanktivorous fish may be useful in attempts to mitigate eutrophication in temperate shallow lakes, it is uncertain whether similar mitigation might be achieved in warmer climates. We compared the responses of zooplankton and phytoplankton communities to climate warming in the presence and absence of fish (Aristichthys nobilis) in a 4-month mesocosm experiment at subtropical temperatures. We hypothesized that 1) fish and phytoplankton would benefit from warming, while zooplankton would suffer in fish-present mesocosms and 2) warming would favor zooplankton growth but reduce phytoplankton biomass in fish-absent mesocosms. Our results showed significant interacting effects of warming and fish presence on both phytoplankton and zooplankton. In mesocosms with fish, biomasses of fish and phytoplankton increased in heated treatments, while biomasses of Daphnia and total zooplankton declined. Warming reduced the proportion of large Daphnia in total zooplankton biomass, and reduced the zooplankton to phytoplankton biomass ratio, but increased the ratio of chlorophyll a to total phosphorus, indicating a relaxation of zooplankton grazing pressure on phytoplankton. Meanwhile, warming resulted in a 3-fold increase in TP concentrations in the mesocosms with fish present. The results suggest that climate warming has the potential to boost eutrophication in shallow lakes via both top-down (loss of herbivores) and bottom-up (elevated nutrient) effects. However, in the mesocosms without fish, there was no decline in large Daphnia or in total zooplankton biomass, supporting the conclusion that fish predation is the major driver of low large Daphnia abundance in warm lakes. In the fishless mesocosms, phytoplankton biomass and nutrient levels were not affected by temperature. Our study suggests that removing fish to mitigate warming effects on eutrophication may be potentially beneficial in subtropical lakes, though the rapid recruitment of fish in such lakes may present a challenge to success in the long-term.

Contrasting patterns of macroinvertebrates inshore vs. offshore in a plateau eutrophic lake: Implications for lake management

Worldwide there has been deterioration of lakeshore habitat and increasing eutrophication. These stresses have impacted littoral macroinvertebrate communities. However, bioassessment and rehabilitation have been largely carried out offshore, and the inshore macroinvertebrates have received less attention especially in shallow plateau lakes. In this study, we compared inshore and offshore macroinvertebrate communities in a shallow plateau lake, Lake Dianchi, China. The environmental parameters determining the distribution of macroinvertebrates were analyzed with partial redundancy analysis. Our results showed that macroinvertebrate communities differed significantly between inshore and offshore. Taxonomic richness was much higher inshore than offshore, due to higher habitat heterogeneity. By contrast, both density and biomass inshore were significantly lower than those of offshore. Generally, vegetation and substrate type were the key environmental parameters shaping macroinvertebrate communities. Eutrophication exerted great effect on offshore communities, while its impacts on inshore communities varied spatially. Shoreline degradation and seasonal eutrophication effects resulted in the limited density and biomass of inshore communities. Our results emphasized the significance of inshore habitats for macroinvertebrates in Lake Dianchi, and provided important implications for bioassessment and ecological rehabilitation in shallow lakes.

Recent Sedimentation Rates of Shallow Lakes in the Middle and Lower Reaches of the Yangtze River: Patterns, Controlling Factors and Implications for Lake Management

Significantly increased sedimentation rates (SRs) in lakes worldwide in recent decades due to higher inputs of silt and eutrophication have led to significant environmental problems such as lake size diminishment and degraded water quality. Many lakes in the middle and lower reaches of the Yangtze River basin (MLYB) have followed this pattern. For effective lake management, it is essential to understand the pattern and drivers of SRs in these lakes. Fourteen typical lakes in the MLYB were chosen to examine the spatiotemporal patterns of SRs and identify the drivers over different time periods. Since 1900, SRs increased from <0.2 to 0.3–0.6 g·cm−2·year−1, particularly notable during 1930–1990. Combined with climatic factors, SR correlated negatively with lake (catchment) size and abundance of aquatic vegetation, whereas other lake features including nutrient status did not contribute significantly to the variation in SRs, due to the fast decomposition processes of organic matter in shallow lakes. Detrimental land use practices especially reclamation for croplands and rapid urbanization was revealed to elevate SRs pronouncedly. We propose various management strategies aiming to maintain SR reference condition at ~0.16 ± 0.08 g·cm−2·year−1, which is analogous to the SR value between 1850 and 1900.

Quantification of Nutrient Assimilative Capacity of Chara (sp.) in a Previously Hypereutrophic Lake in Southwest Florida (USA): Implications for Lake Management

Quantification of Nutrient Assimilative Capacity of Chara (sp.) in a Previously Hypereutrophic Lake in Southwest Florida (USA): Implications for Lake Management

Effects of benthic-feeding common carp and filter-feeding silver carp on benthic-pelagic coupling: Implications for shallow lake management

Benthic–pelagic coupling is a key factor in the dynamics of shallow lakes. A 12-week mesocosm experiment was set up to test the hypotheses that benthic-feeding common carp (Cyprinus carpio) reduce the growth of benthic algae and promote eutrophication and that filter-feeding silver carp (Hypophthalmichthys molitrix) stimulate benthic algae growth and promote the establishment of a clear-water state. Compared to the controls, the common carp treatment had higher concentrations of total nitrogen (TN) and total phosphorus (TP) in the water column, higher biomass of pelagic algae (measured as chlorophyll a), higher total suspended solids (TSS) concentrations, lower light intensity, and lower biomass of benthic algae at the sediment surface. Silver carp did not change the chlorophyll a of pelagic algae relative to the controls, but they did decrease the biomass of benthic algae and increase TP and TSS. A microcosm experiment using 32P radiotracer was conducted to examine effects of the two carp species on the release of sediment phosphorus (P). The P release to the water column was higher with common carp present than without common carp. This was not the case in the silver carp experiments. Our findings show that both common carp and silver carp deteriorate water quality by increasing TP and TSS concentrations and decreasing the biomass of benthic algae at the sediment surface. Common carp had a larger negative effect on water quality than silver carp, perhaps because only common carp enhanced P release from the sediment. The implications for lake management are that removal of both common carp and silver carp from shallow lakes may enhance the growth of benthic algae and help promote the establishment of a clear-water state.

Size-dependent feeding of omnivorous Nile tilapia in a macrophyte-dominated lake: implications for lake management

Some species or size classes of omnivorous/herbivorous fish in (sub) tropical lakes feed on periphyton and phytoplankton, potentially promoting growth of macrophytes via reduced shading. Others feed on macrophytes, thereby enhancing the risk of having a turbid phytoplankton-dominated system in shallow lakes. Nile tilapia (Oreochromis niloticus), an abundant species in many warm lakes, feed on periphyton, phytoplankton, and macrophytes depending on their size and may therefore have a size-dependent effect on lake ecosystems. We conducted a C–N stable isotope analysis on different size-classes of tilapia and their potential prey to determine their food sources in a tropical eutrophic shallow lake dominated by submerged macrophytes. The shares of the dominant macrophyte, Vallisneria natans, periphyton, and seston in the diet of fish averaged approx. 54, 26, and 20%, respectively. Large-bodied specimens fed mainly on macrophytes, while small-bodied specimens were more dependent on periphyton, seston, or detritus. The results were confirmed by subsequent stomach analysis. We conclude that small-sized tilapia promote macrophyte growth by removing periphyton and seston, whereas large-bodied individuals may restrict macrophyte development. Selective removal of large-bodied tilapia might, therefore, stimulate the development of submerged macrophytes and promote or maintain a clear water state in eutrophic shallow lakes with abundant tilapia.

Identification of a biomanipulation‐driven regime shift in Lake Vesijärvi: implications for lake management

Summary The biomanipulation of Lake Vesijärvi in southern Finland putatively changed the lake ecosystem resulting in a clear‐water state, but the dynamics behind the observed change remained unverified. We used a general analytical approach to identify abrupt transitions in the long‐term monitoring data of Lake Vesijärvi. Methods included the identification of breakpoints in chlorophyll a (response variable), in total phosphorus (TP; key driver) and in large‐bodied cladocerans (feedback mechanism of biomanipulation). In addition, we characterised the frequency distribution and temporal variance of the response variable, as well as the interaction between TP and chlorophyll a. According to long‐term records, biomanipulation resulted in two distinct states: (i) a eutrophic state, where chlorophyll a and TP were linearly correlated and (ii) a mesotrophic state, where the key driver and response variables were not significantly correlated. The changed relationship between the key driver and response variables, together with the increase in the body size of cladocerans, suggested a hysteresis‐type transition phase. However, the frequency distribution and the temporal variance of chlorophyll a agreed also with a threshold‐type of transition. Zooplankton seemed to be more important in maintaining the clear‐water state than previously reported. Our results highlight the role of long‐term monitoring data and the characterisation of abrupt transitions in ecosystem interactions as tools for sustainable management of lake ecosystems.

Variation in chlorophyll a to total phosphorus ratio across 94 UK and Irish lakes: Implications for lake management

Eutrophication is the most widespread pressure impacting on lakes worldwide and, in general, its control is underpinned by the premise that algal biomass is regulated by phosphorus availability. This paper aims to demonstrate that not all lakes will conform to the underlying principle of the Chl:TP relationships using variables collected widely in lake monitoring programmes across the world (i.e. total phosphorus (TP) and chlorophyll a (Chl) concentrations). The ratio of annual mean Chl and TP concentrations in 94 lakes (2007 and 2008) was used as a measure of the efficiency with which TP is transferred into algal biomass (i.e. as an indicator of P limitation) to investigate the validity of the phosphorus reduction approach. Chl:TP ratios ranged from 0.02 to 0.84 in 2007 and from 0.03 to 0.96 in 2008. Chl and TP values were positively correlated (p < 0.05) with alkalinity, and negatively correlated with depth and surface area, in both years. In general, mean annual Chl and TP concentrations increased as alkalinity increased and depth decreased. However, Chl:TP ratio was highest in high alkalinity lakes in 2007, and moderate alkalinity lakes in 2008. Our results indicate that the use of TP water quality targets alone is insufficient to accurately manage eutrophication pressures at the lake specific scale, and that a wider range of ecological and ecosystem service evaluation targets would provide a more comprehensive assessment of management needs. The wide range of Chl:TP ratio values reported in this study suggests that, although reducing TP concentrations in lakes is undoubtedly a sensible approach to eutrophication management in many cases, TP reductions alone may not result in the expected reductions in phytoplankton biomass in all lakes.

Persistence of protected, vulnerable macrophyte species in a small, shallow eutrophic lake (eastern Poland) over the past two centuries: Implications for lake management and conservation

The developmental history of shallow, eutrophic Lake Głębokie Uścimowskie, eastern Poland, spanning the last 180 years, was studied using analyses of pollen, plant macrofossils, diatoms, chlorophyll and carotenoid pigments, Cladocera, Chironomidae and geochemistry from lead-210 dated sediment cores. The lake was colonised by macrophytes and eutrophic through the whole investigation period, but from 1950 AD the trophic status increased slowly and eutrophication accelerated after 1980 AD, leading to hypertrophy. Despite this eutrophication history, macro- and microfossils indicated the continuing presence of Isoëtes lacustris spores and Elatine hydropiper seeds in the sediments of the lake, even though neither species were encountered in the recent and present-day lake macrophyte surveys. Both the species are classified as vulnerable (IUNC List) in Poland and are presently deemed extinct due to eutrophication in the Łęczna-Włodawa Lake District. We conclude the silica-rich substrates (51–77%), low in calcium (<1%) and organic matter (7–21%) in the lake were crucial for the survival of soft-water species like I. lacustris and species that prefer sandy littoral habitats like E. hydropiper. We also propose that water level fluctuations were important in modifying the extent of the littoral zone and sorting the substrate and thus in maintenance of appropriate habitat for these rare species. Therefore, substrate type and hydrological factors appear to be important to conservation of rare species in this lake.