Evaluation of algal chlorophyll and nutrient relations and the N:P ratios along with trophic status and light regime in 60 Korea reservoirs

Authors

Md Mamun, Seokcheol Kwon, Jeong-Eun Kim, Kwang-Guk An

The present study aimed to determine the spatial and temporal variations in trophic state and identify potential causes for these variations in 60 Korean reservoirs. Empirical models were developed using the relations of nutrients (total phosphorus, TP, and total nitrogen, TN) with chlorophyll-a (CHL-a) for efficient lake managements. The empirical models indicated that TP was the key regulating factor for algal growth in agricultural (R² = 0.69) and power generation (R² = 0.50) reservoirs. The CHL-a:TP and TN:TP ratios, indicators of phosphorus limitation, were used to validate the phosphorus reduction approach. The mean CHL-a:TP ratio of agricultural reservoirs was 0.60, indicating that algal chlorophyll is potentially limited by TP than any other factors. Agricultural, multipurpose, and power generation reservoirs, based on the N:P ratios, were more P- limited systems than natural lakes and estuarine reservoirs. The trophic state index (TSI) of Korean reservoirs varied between mesotrophy to hypereutrophy based on values of TSI (TP), TSI (CHL-a), and TSI (SD). Agricultural reservoirs were hypereutrophic using the criteria of TSI (CHL-a) and blue-green algae dominated the algal community. Analysis of trophic state index deviation (TSID) indicated that agricultural reservoirs were primarily P limited and other factors had minor effect. In contrast, the trophic status of estuarine and power generation reservoirs and natural lakes was largely modified by non-algal turbidity. Our outcomes may be effectively used for Korean lakes and reservoirs management.

A risk assessment method for remote sensing of cyanobacterial blooms in inland waters

Authors

Nengcheng Chen, Siqi Wang, Xiang Zhang, Shangbo Yang

The widespread occurrence of Cyanobacterial blooms (CABs) in inland waters is a typical and severe challenge for water resources management and environment protection. An accurate and spatially continuous risk assessment of CABs is critical for prediction and preparedness in advance. In this study, a multivariate integrated risk assessment (MIRA) method of CABs in inland waters was proposed. MIRA was simplified with the trophic levels, cyanobacterial and other aquatic plant condition using remote sensing indexes, including the Trophic State Index (TSI), Floating Algae Index (FAI) and Cyanobacteria and Macrophytes Index (CMI). First, the dates of risk assessment were carefully selected based on TSI. Then, we obtained the trophic levels, cyanobacterial, and other aquatic plant condition of water using TSI, CMI and FAI on the selected date, and further scored them pixel by pixel to quantify the risk value. Finally, the risk of CABs in water was accurately assessed based on the pixel risk value. Based on Landsat 8 OLI dataset, MIRA was executed and validated in three different lakes of Wuhan urban agglomeration (WUA) with different trophic states. The results demonstrated that the risk of CABs in Lake LongGan was overall higher than that in Lake LiangZi and Lake FuTou. And the risk of CABs in the east part of Lake LongGan was higher than the other parts. Seasonally, the risk level ranking in Lake LiangZi was the highest in summer, while lowest in winter. However, the seasonal risk ranking was spring, summer, autumn, and winter in Lake LongGan. Based on the comparisons with monthly water quality classification data and results of the existing study, including trophic level, ecology risk, and algal extent, the MIRA method was valuable for accurate and spatially continuous identifying the risk of CABs in inland waters with potential eutrophication trends.

Composition characterization and biotransformation of dissolved, particulate and algae organic phosphorus in eutrophic lakes

Authors

Weiying Feng, Fang Yang, Chen Zhang, Jing Liu, Fanhao Song, Haiyan Chen, Yuanrong Zhu, Shasha Liu, John P. Giesy

Characteristics and transformation of organic phosphorus in water are vital to biogeochemical cycling of phosphorus and support of blooms of phytoplankton and cyanobacteria. Using solution ³¹P nuclear magnetic resonance (NMR), combined with field surveys and lab analyses, composition and structural characteristics of dissolved phosphorus (DP), particulate phosphorus (PP) and organic P in algae were studied in two eutrophic lakes in China, Tai Lake and Chao Lake. Factors influencing migration and transformation of these constituents in lake ecosystems were also investigated. A method was developed to extract, flocculate and concentrate DP and PP from lake water samples. Results showed that orthophosphate (Ortho-P) constituted 32.4%–81.3% of DP and 43.7%–54.9% of PP, respectively; while monoester phosphorus (Mono-P) was 13.2%–54.0% of DP and 32.9%–43.7% of PP, respectively. Phosphorus in algae was mostly organic P, especially Mono-P, which was ≥50% of TP. Environmental factors and water quality parameters such as temperature (T), electrical conductivity (EC), pH, secchi depth (SD), dissolved oxygen (DO), chemical oxygen demand (COD_cr), chlorophyll-a (Chl-a), affected the absolute and relative concentrations of various P components in the two lakes. Increased temperature promoted bioavailable P (Ortho-P and Mono-P) release to the lake waters. The results can provide an important theoretical basis for the mutual conversion process of organic P components between various media in the lake water environment.

Trophic control changes with season and nutrient loading in lakes

Authors

Tanya L. Rogers Stephan B. Munch Simon D. Stewart Eric P. Palkovacs Alfredo Giron‐Nava Shin‐ichiro S. Matsuzaki Celia C. Symons

Experiments have revealed much about top‐down and bottom‐up control in ecosystems, but manipulative experiments are limited in spatial and temporal scale. To obtain a more nuanced understanding of trophic control over large scales, we explored long‐term time‐series data from 13 globally distributed lakes and used empirical dynamic modelling to quantify interaction strengths between zooplankton and phytoplankton over time within and across lakes. Across all lakes, top‐down effects were associated with nutrients, switching from negative in mesotrophic lakes to positive in oligotrophic lakes. This result suggests that zooplankton nutrient recycling exceeds grazing pressure in nutrient‐limited systems. Within individual lakes, results were consistent with a ‘seasonal reset’ hypothesis in which top‐down and bottom‐up interactions varied seasonally and were both strongest at the beginning of the growing season. Thus, trophic control is not static, but varies with abiotic conditions – dynamics that only become evident when observing changes over large spatial and temporal scales.

The influences of historic lake trophy and mixing regime changes on long-term phosphorus fraction retention in sediments of deep eutrophic lakes: a case study from Lake Burgäschi, Switzerland

Authors

Luyao Tu, Paul Zander, Sönke Szidat, Ronald Lloren, and Martin Grosjean

Hypolimnetic anoxia in eutrophic lakes can delay lake recovery to lower trophic states via the release of sediment phosphorus (P) to surface waters on short timescales in shallow lakes. However, the long-term effects of hypolimnetic redox conditions and trophic state on sedimentary P fraction retention in deep lakes are not clear yet. Hypolimnetic withdrawal of P-rich water is predicted to diminish sedimentary P and seasonal P recycling from the lake hypolimnion. Nevertheless, there is a lack of evidence from well-dated sediment cores, in particular from deep lakes, about the long-term impact of hypolimnetic withdrawal on sedimentary P retention. In this study, long-term sedimentary P fraction data since the early 1900s from Lake Burgäschi provide information on benthic P retention under the influence of increasing lake primary productivity (sedimentary green-pigment proxy), variable hypolimnion oxygenation regimes (Fe∕Mn ratio proxy), and hypolimnetic withdrawal since 1977. Results show that before hypolimnetic withdrawal (during the early 1900s to 1977), the redox-sensitive Fe∕Mn-P fraction comprised ∼50 % of total P (TP) in the sediment profile. Meanwhile, long-term retention of total P and labile P fractions in sediments was predominantly affected by past hypolimnetic redox conditions, and P retention increased in sedimentary Fe- and Mn-enriched layers when the sediment-overlaying water was seasonally oxic. However, from 1977 to 2017, due to eutrophication-induced persistent anoxic conditions in the hypolimnion and to hypolimnetic water withdrawal increasing the P export out of the lake, net burial rates of total and labile P fractions decreased considerably in surface sediments. By contrast, refractory Ca–P fraction retention was primarily related to lake primary production. Due to lake restoration since 1977, the Ca–P fraction became the primary P fraction in sediments (representing ∼39 % of total P), indicating a lower P bioavailability of surface sediments. Our study implies that in seasonally stratified eutrophic deep lakes (like Lake Burgäschi), hypolimnetic withdrawal can effectively reduce P retention in sediments and potential for sediment P release (internal P loads). However, after more than 40 years of hypolimnetic syphoning, the lake trophic state has not improved nor has lake productivity decreased. Furthermore, this restoration has not enhanced water column mixing and oxygenation in hypolimnetic waters. The findings of this study are relevant regarding the management of deep eutrophic lakes with mixing regimes typical for temperate zones.

Effect of eutrophication and humification on nutrient cycles and transfer efficiency of matter in freshwater food webs

Authors

Maciej Karpowicz, Piotr Zieliński, Magdalena Grabowska, Jolanta Ejsmont-Karabin, Joanna Kozłowska & Irina Feniova

We evaluated how eutrophication and humification impacted nutrient cycles and the efficiency of carbon transfer in the planktonic food webs of 12 lakes in north-eastern Poland that differed in trophic state. Our results indicated that the effectiveness of carbon transfer between phytoplankton and zooplankton varied from 0.0005% to 0.14%, which is much lower than the theoretical 10%. The highest efficiency of carbon transfer occurred in the mesotrophic lakes due to the higher hypolimnetic zooplankton production, while the lowest efficiency was observed in the dystrophic lakes and in one eutrophic lake that was dominated by cyanobacteria. Inedible algae (e.g. Gonyostomum semen) and cyanobacteria appeared to be the main factors reducing the efficiency of the transfer of matter in pelagic food webs. The results of our study showed that plankton communities are a key component of the nutrient cycle in freshwater food webs. Phytoplankton were a very effective nitrogen sink, and in the mesotrophic lakes, up to 99% of the total nitrogen was sequestrated in phytoplankton. As a result, there was a depletion of inorganic nitrogen in the upper water layer. Furthermore, zooplankton were an important phosphorus sink, thus significantly influencing the nutrient cycles.

Effect of eutrophication and humification on nutrient cycles and transfer efficiency of matter in freshwater food webs

Authors

Maciej Karpowicz, Piotr Zieliński, Magdalena Grabowska, Jolanta Ejsmont-Karabin, Joanna Kozłowska & Irina Feniova

We evaluated how eutrophication and humification impacted nutrient cycles and the efficiency of carbon transfer in the planktonic food webs of 12 lakes in north-eastern Poland that differed in trophic state. Our results indicated that the effectiveness of carbon transfer between phytoplankton and zooplankton varied from 0.0005% to 0.14%, which is much lower than the theoretical 10%. The highest efficiency of carbon transfer occurred in the mesotrophic lakes due to the higher hypolimnetic zooplankton production, while the lowest efficiency was observed in the dystrophic lakes and in one eutrophic lake that was dominated by cyanobacteria. Inedible algae (e.g. Gonyostomum semen) and cyanobacteria appeared to be the main factors reducing the efficiency of the transfer of matter in pelagic food webs. The results of our study showed that plankton communities are a key component of the nutrient cycle in freshwater food webs. Phytoplankton were a very effective nitrogen sink, and in the mesotrophic lakes, up to 99% of the total nitrogen was sequestrated in phytoplankton. As a result, there was a depletion of inorganic nitrogen in the upper water layer. Furthermore, zooplankton were an important phosphorus sink, thus significantly influencing the nutrient cycles.

Estimation of lake ecological quality from Sentinel-2 remote sensing imagery

Authors

Gary Free, Mariano Bresciani, Wayne Trodd, Deirdre Tierney, Shane O’Boyle, Caroline Plant & Jenny Deakin

The Water Framework Directive requires European states to monitor the ecological quality of their lakes. Detailed information on the composition and abundance of biological groups such as aquatic plants (macrophytes) and phytoplankton (including chlorophyll a) must be expressed as an ecological quality ratio (EQR), ranging from 1 (close to reference status) to 0 (bad status). Effort is often focused on gathering this detailed information on selected lakes at the expense of more synoptic approaches that could capture a more holistic assessment of a catchment’s water quality. This could be rectified if remote sensing can provide predictions of ecological quality for unmonitored lakes. We found that data from Sentinel-2 satellites, based on regression model outputs of observed vs estimated results, successfully predicted the macrophyte EQR (R² = 0.77) and the maximum lake depth that macrophytes colonised to (R² = 0.80) but average chlorophyll a was less well predicted (R² = 0.66). Predictions for a test catchment indicated that results were within one ecological assessment class width of measured values for macrophytes. This approach can potentially estimate status for unmonitored lakes in Ireland, be integrated with results on monitored lakes and used to direct resources where needed at national and catchment scales.

 

A new broad typology for rivers and lakes in Europe: Development and application for large-scale environmental assessments

Authors

Anne Lyche Solheim, Lidija Globevnik, Kari Austnes, Peter Kristensen, S. Jannicke Moe, Jonas Persson, Geoff Phillips, Sandra Poikane, Woutervan de Bund, Sebastian Birk

European countries have defined >1000 national river types and >400 national lake types to implement the EU Water Framework Directive (WFD). In addition, common river and lake types have been defined within regions of Europe for intercalibrating the national classification systems for ecological status of water bodies. However, only a low proportion of national types correspond to these common intercalibration types. This causes uncertainty concerning whether the classification of ecological status is consistent across countries. Therefore, through an extensive dialogue with and data provision from all EU countries, we have developed a generic typology for European rivers and lakes. This new broad typology reflects the natural variability in the most commonly used environmental type descriptors: altitude, size and geology, as well as mean depth for lakes. These broad types capture 60–70% of all national WFD types including almost 80% of all European river and lake water bodies in almost all EU countries and can also be linked to all the common intercalibration types. The typology provides a new framework for large-scale assessments across country borders, as demonstrated with an assessment of ecological status and pressures based on European data from the 2nd set of river basin management plans. The typology can also be used for a variety of other large-scale assessments, such as reviewing and linking the water body types to habitat types under the Habitats Directive and the European Nature Information System (EUNIS), as well as comparing type-specific limit values for nutrients and other supporting quality elements across countries. Thus, the broad typology can build the basis for all scientific outputs of managerial relevance related to water body types.

Planktonic indicators of trophic states for a shallow lake (Baiyangdian Lake, China)

Authors

Caihong Tang, Yujun Yi, Zhifeng Yang, Yang Zhou, Teklit Zerizghi, Xuan Wang, Xiuli Cui, Pengyu Duan

Eutrophication in lake ecosystems poses a serious threat to the water quality and function of aquatic ecosystems. The species composition and community structure of plankton change directly with variations in lake trophic states. Seasonal sample collections of phytoplankton, zooplankton and environmental variables were conducted in spring, summer, and fall from a large shallow lake, Baiyangdian Lake, China. The species richness, community composition and temporospatial variations of phytoplankton and zooplankton were analyzed. The lake trophic states were assessed using the comprehensive trophic state index (CTSI) and rotifer trophic state index (TSI_ROT). The results indicated that 69.1% of the lake area showed slight eutrophication, 29.3% showed mesotrophication, and 1.6% showed moderate eutrophication. The Shannon-Wiener diversity index and Pielou evenness index were employed to assess the community diversity of phytoplankton and zooplankton. The dominant taxa and most dominant species of phytoplankton and zooplankton were determined; Cyanophyta and Rotifera were the dominant phytoplankton and zooplankton taxa, respectively. Microcystis sp. and Polyarthra vulgaris were the most dominant species of phytoplankton and zooplankton, respectively. Redundancy analysis (RDA) was applied to identify the key environmental variables that influenced the species, diversity indices and species abundance of phytoplankton and zooplankton. The results showed that ammonia nitrogen (NH₄⁺), total nitrogen (TN), total phosphorus (TP), and dissolved oxygen (DO) were the main environmental factors influencing the species abundance and diversity. The current lake plankton species number and diversity index were lower than those in past decades, as determined by comparing the community characteristics of phytoplankton and zooplankton with historical records. Comparisons of TN:TP ratios with those of other lakes suggested that nitrogen was the limiting nutrient for lake eutrophication. Baiyangdian Lake could have a high potential for eutrophication based on the environmental and ecological characteristics of the lake.