Trophic State Index Research Articles

Patterns of effects of land-use structure on lake water quality in coastal lake catchments of the southern Baltic Sea

This study investigated potential relationships between land-use structure in the catchments of six southern Baltic coastal lakes that differ in the level of hydrological connection with the sea and the lakes’ trophic states. Our results indicate that three types of catchments can be distinguished, each of which has a high contribution of agricultural areas, plus: (i) considerable contributions of wetlands and water bodies (C1); (ii) a large contribution of wooded and seminatural habitats (C2); or (iii) a considerable contribution of artificial surfaces (C3). Correlations were analysed between land-use types and single-parameter Carlson's trophic state indices of lakes (TSIChl, TSITP, TSISD, TSITOC). Type C2 clearly differed from the others and was linked with the lowest trophic state index values. The other two catchment types were similarly related to the fertility of the coastal lakes. The results show that the analysed lakes’ levels of connection with the sea do not affect the trophic state of their waters. Catchment structure, analysed using CORINE Land Cover data, is significantly linked with TP and TOC values, but it does not relate to Secchi depth or chlorophyll content of water in the lakes. Wetlands (especially peat bogs) in the catchment area most strongly reduced the phosphorus and organic carbon content of lake water. Furthermore, comparable contributions of natural vs. anthropogenic components (∼1:1) are associated with a lower trophic state of water. The presented results may be important for shaping the proper management of various catchment types in the future, especially when implementing climate change mitigation strategies.

Management actions mitigate the risk of carbon dioxide emissions from urban lakes

Lakes are recognized as important sources of carbon dioxide (CO2) emissions, which vary greatly across land use type. However, CO2 emissions from lakes in urban landscapes are generally overlooked despite their daily connections to human activity. Furthermore, the role of management actions in CO2 emissions remained unclear mostly because of the lack of long-term observations. Here, the CO2 partial pressure (pCO2) from two urban lakes (Lake Wuli and Lake Donghu) in eastern China were investigated based on 16-year (2002–2017) field measurements. This long-term measurements showed the annual mean pCO2 were 1150 ± 612 μatm for Lake Wuli and 1143 ± 887 μatm for Lake Donghu, with corresponding estimated flux of 21.12 ± 19.60 mmol m−2 d−1 and 16.42 ± 20.39 mmol m−2 d−1, respectively. This indicates significant CO2 evasion into the atmosphere. Strong links between CO2 and human-derived nutrients (e.g., ammonium) and dissolved organic carbon, dissolved oxygen, and trophic state index were found. Although pCO2 was relatively uniform across sites and seasons in each lake, substantial inter-annual variability with significant decreasing trends were found. The decrease in annual CO2 can be partly explained by the reduction of pollutant loadings with management actions, which held the hypotheses that management actions mitigated the CO2 emission risks. Overall, management actions (e.g., ecological restoration and municipal engineering) should be considered for better understanding the roles of anthropogenic aquatic ecosystems in carbon cycle.

Promoting effect and mechanism of residual feed organic matter on the formation of cyanobacterial blooms in aquaculture waters

Cyanobacterial blooms and eutrophication often occur in aquaculture waters where feeds are used. We hypothesize that residual feed organic matter (RFOM) can contribute to increased dissolved reactive phosphorus (SRP) concentrations in the water column by altering sediment phosphorus release characteristics (PRCS), including phosphorus fractions (i.e., Fe–P) and phosphorus adsorption (i.e., Qmax, EPC0), which is ultimately conducive to the formation of cyanobacteria blooms. Three types of aquaculture waters that were never feeding (NF), long-term feeding (LF), and stopped feeding (SF) for several years were studied to verify the above hypothesis. The results showed that the concentrations of SRP and chlorophyll-a in LF were significantly higher than those in SF and NF (P < 0.05). RFOM significantly affects PRCS with a power function relationship with EPC0 and a linear relationship with Qmax. Similarly, SRP in the water column was positively correlated with PRCS (i.e., Fe–P, EPC0), cyanobacterial biomass, and trophic state index (P < 0.01). This suggested that SRP may be an essential link between sediment and algal community structure. Simulation experiments further confirmed the above hypothesis, With the increase in RFOM (94.36 g/kg), PRCS (i.e., Fe–P, EPC0, and Qmax) increased significantly, which were 6.60, 282.36, and 2.47 times that of the control group, respectively. The sediment bacterial community and the partial least squares path model indicated that RFOM could regulate the SRP concentration in the water body and promote the formation of cyanobacterial blooms through PRCS, in which Firmicutes played an important role. This study revealed the driving process and mechanism of feeding behavior on the formation of cyanobacterial blooms and eutrophication in aquaculture waters, which provided a basis for the health management and cleaning strategy of aquaculture waters.

A comprehensive evaluation of water quality and its potential health risks using physicochemical indices in coastal areas of the Gulf of Suez, Red Sea

The Gulf of Suez plays a significant role in Egypt's economy and strategic position in the region, making it a critical waterway domestically and internationally due to being an essential hub for Egypt's oil and gas industry, housing numerous offshore oil and gas fields in the region. This paper aimed to comprehensively present the environmental status of the Gulf of Suez, the Red Sea, and pollution sources using one of the most fundamental ways to evaluate a water body. The Water Quality Index (WQI) measures nitrate levels in marine water and determines their potential harm to human health and the ecosystem. Excessive amounts of nitrate can pose non-carcinogenic health risks. Trophic state index (TSI), trophic index (TRIX), and Organic Pollution Index (OPI) are practical applications for surface water quality investigation and categorization based on contamination level. Principal Component Analysis (PCA), and Cluster Analysis (CA), were used to get better information for the studies on the water quality of surface waters. This study tested 38 subsurface locations during February 2021 for physical, chemical, microbiological, and nutritional salts. The WQI revealed that 71.23% of seawater samples were classified as having good water quality. However, TRIX and TSI metrics indicated eutrophication, with an average mean of 55.20, categorizing the water quality fairly. OPI values ranged between (3.50–3.75) which can be classified as moderate water quality. Finally, the current study's findings indicated the NO3− non-carcinogenic health hazards (HQ < 1) in all groups, but children are at a higher risk of NO3− exposure. Therefore, it can be concluded that Periodic assessments of water quality and strict regulations are necessary to safeguard this vital resource from pollution and ensure the well-being of future generations.

Limnological features and water-quality changes of two Ethiopian Rift Valley lakes, Lake Abaya and Lake Chamo

We conducted a study in Lake Abaya and Lake Chamo, the two largest Ethiopian Rift Valley lakes, between 2016 and 2019, to evaluate their limnological features and infer longer-term changes in some water-quality parameters. Data generated through in situ measurements and laboratory analyses of physico-chemical parameters and the plankton communities were compared with results from the literature. Turbidity, salinity, nitrates and soluble reactive phosphorous showed an increasing trend in Lake Abaya, while in Lake Chamo conductivity, salinity, nitrates and soluble reactive phosphorous showed an increasing trend. In both lakes the water transparency and chlorophyll a concentration showed a declining trend. Despite higher available nutrients in Lake Abaya compared with Lake Chamo, higher turbidity with suspended solids contributed to lower chlorophyll-a concentrations and lower zooplankton abundance. The abundances of rotifers and crustaceans were lower in Lake Abaya compared with Lake Chamo. The mean trophic state index using total phosphorus, Secchi depth and chlorophyll-a shows that both lakes are in a eutrophic state. Our findings are consistent with previous studies and indicate that changes in major limnological features are a signal to take intervention measures to prevent further ecological degradation and to sustain the ecological services and livelihoods of fishers who are directly dependent on the lakes.

Are rotifer indices suitable for assessing the trophic status in slow-flowing waters of canals?

Abstract Zooplankton indicators based on rotifers (TSIROT) and an indicator based on Secchi disk visibility (TSISD) were used to assess trophic state changes in artificial, slow-flowing, and stagnant canal waters. The study was conducted in the summers of 2019, 2021, and 2022 in the Bydgoszcz Canal and the Noteć Canal (Poland). Water samples were taken from five sites once in the month of July and once in August. In terms of the species number and density, rotifers dominated among zooplankton (at almost all sites), which reflected the high trophic state. Our results showed statistically significant correlations between TSIROT and TSISD as well as between the individual indicators TSIROT1 (Rotifer numbers), TSIROT2 (Rotifer biomass), TSIROT3 (bacterivorous numbers of rotifers), TSIROT6 (rotifers indicating high trophic state), and TSISD. According to our study, the presented indices most likely determine the trends between TSIROT cumulative and TSISD in the studied canals. Similarly to previous studies performed on lakes and small reservoirs, zooplankton constituted a useful indicator of trophic state. It seems that, for stagnant and slowly flowing waters of canals such as the Bydgoszcz Canal and the Noteć Canal, the method of zooplankton trophic status indicators based on rotifers may be applied.

Spatio-temporal evolution of eutrophication and water quality in the Turawa dam reservoir, Poland

The objectives of the article are: to assess spatio-temporal evolution of eutrophication and water quality of the Turawa dam reservoir, located in south-western Poland on the Mała Panew River; to identify location and relationship between potential sources of physicochemical pollution related to the progressing process of eutrophication; and to determine trophic status and water quality indices of the selected research object. The analysis (Mann–Whitney U test, PCA, HCA, Spearman correlation matrix) showed a high susceptibility of the reservoir to eutrophication processes, especially due to the influence of dangerous loads of compounds emerging from areas with high tourist intensity and pollutants flowing from the Mała Panew River. The parameters deteriorating the ecological status were TP, DO, BOD5, and COD. Considering the cumulative results of water quality indices for the period 1998–2020, the average water quality was in classes II or III. A noticeable deterioration appeared in water quality for the years 2016–2020, which proves the progressing eutrophication in the Turawa reservoir. In 1998–2020, the reservoir was classified as eutrophic or mesoeutrophic based on the calculated three trophic status indices. This article would help in developing a strategy for dealing with water blooms, a reliable system for monitoring pressures causing eutrophication, and optimal technologies for the reconstruction of multifunctional reservoirs.

Fuzzy-based global water quality assessment and water quality cells identification using satellite data

The water environmental impact assessment and management programs increasingly rely on accurate and quantitative estimates of water quality parameters through remote sensing, owing to the limitation of the time-consuming field-based approaches. Numerous studies have utilised the remote-derived water-quality products and existing water quality index WQI models, but they are typically site-specific and yield significant errors for the accurate assessment and monitoring of coastal and inland water bodies. This study presents a generalized WQI model that incorporates a flexible number of parameters, simplifying them to produce comprehensive water quality index values with the fuzzy logic approach. To derive these index values, three major water quality parameters such as Chl, TSS and aCDOM443 were estimated using new remote-sensing models, and the corresponding indices Trophic State Index (TSI), Total Suspended Solids Index (TSSI) and CDOM Index (CI) were produced by a generalized index model. Finally, WQI products were derived based on the Mamdani-based Fuzzy Inference System (FIS) and individual contribution of the water quality parameters to WQI was analysed to establish ‘Water Quality Cells’ WQcells, which are represented by the dominant WQ parameter. The new models were tested on MODIS-Aqua and Sentinel-3 OLCI data in different regional and global oceanic waters. Further, a time series analysis was performed in regional coastal oceanic waters (along the Indian coast) to study the seasonal variations of individual water quality parameters and WQI over the period from 2011 to 2020. The results demonstrated that the FIS is efficient in handling the parameters with varying units and their relative importance. The water quality cells were identified in the bloom-dominated (Arabian Sea), TSS-dominated (Point Calimere, India and Yangtze River estuary, China) and CDOM-dominated (South Carolina coast, USA) regions. The time series analysis revealed that the water quality of the Indian coast exhibits cyclic seasonal variations due to the annual occurrence of the south-west and north-east monsoons. These results are critical for monitoring and assessing the quality of surface waters in coastal and inland environments and enabling water resources managers to formulate and implement management plans for a variety of water bodies cost-effectively.

Spatial and seasonal variations in nutrient load and trophic status of Ganga and Yamuna rivers in Uttar Pradesh, India

Abstract Nutrient loading in aquatic systems from anthropogenic sources is a worldwide concern. The Ganga is the most important river in India, but pollution is currently severely threatening its biodiversity and long-term environmental viability. Water samples were taken from 36 locations along the length of the Ganga and Yamuna rivers in Uttar Pradesh and analysed for nutrient concentration to evaluate the nutrient load, eutrophication danger, and river trophic status. The average concentration of NO3-N, PO4-P, NH4-N, and SiO2-Si exceeded the values in unpolluted rivers, indicating the contribution of anthropogenic sources. The concentration of NO3-N and NH4-N showed significant spatial variation, and PO4-P showed significant seasonal variation in the study area. The DIN/DIP ratio in the study area exceeded 16:1, indicating a phosphate-limiting condition for phytoplankton development. The DSi/DIN value showed a declining trend in the downstream region of both rivers with average values &amp;lt;1, indicating nitrate pollution leading to eutrophic conditions. The Indicator for Coastal Eutrophication Potential (ICEP) showed a positive value, indicating that the Ganga and Yamuna rivers in Uttar Pradesh were eutrophic due to nitrogen pollution. Trophic State Index (TSI) values indicated that super-eutrophic conditions existed in the Ganga River (65.62) and hypereutrophic conditions existed in the Yamuna River (75.55) in Uttar Pradesh.

Water quality assessment for Northern Egyptian lakes (Bardawil, Manzala, and Burullus) using NSF-WQI Index

Egyptian Lakes are received different organic and inorganic pollutants from treated and untreated drainage effluent. Forty-five surface water samples from 15 locations were collected in June 2018 from Bardawil, Manzala, and Burullus lakes in northern Egypt. The collected samples measured nutrient salts (NH3, NO2, NO3, and PO4) and some metal ions (Cd, Pb, Cu, and Zn). Furthermore, several instruments are used for managing and organizing data on the total quality of water bodies with risk factors related to heavy metal pollution. This research aimed to apply the National Science Foundation’s WQI (NSF-WQI) and metal pollution index (MPI) to estimate water quality status and degree of pollution in three Northern Lakes in Egypt. The results indicated that Manzala Lake had the greatest concentration of nutritional salts (7.0, 3.8, 3.2 and 5.6 mg/L) for NH4, NO2, NO3 and PO4, respectively. Furthermore, the same order recorded for the mean levels of metal ions (Cd, Pb, Cu, and Zn) were (1.69, 0.29, 3.58 and 20.38 μg/l). In contrast, Bardawil Lake had the lowest values. Trophic Status Index TSIs of Bardawil Lake revealed that it is eutrophic with mean values (69.73), whilst those of Manzala and Burullus Lakes revealed that they are hypertrophic with mean values (90.68–86.20). WQI of Bardawil Lake was assessed as a good rating (92.01) and Excellent by NSF-WQI (95.18) according to WHO. On the other hand, Manzala and Burullus Lakes were rated as very bad and unfit. Manzala Lake was deemed unsafe for human consumption because it tested higher on pollution indices (MI, PI and MPI > 1 are polluted with slightly affected than Bardawil and Burullus lakes. This was due to the enormous quantities of human, animal, and industrial wastes dumped into Manzala Lake.

PRELIMINARY DIAGNOSIS AND WATER QUALITY OF THE PORTEIRAS STREAM IN AN URBAN STRETCH OF PETROLINA-PE

Soil use and occupation alter the physicochemical and biological processes of aquatic ecosystems. Urban streams are fundamental components of the macro-drainage system of cities; however, with the advance of urbanization, most streams are modified to the point that they are no longer recognized as streams but as sewage receptors. Physical diagnosis and monitoring of water quality are essential to understand the trophic state of these ecosystems in relation to environmental impacts associated with urbanization. From this perspective, this study aimed to diagnose the physical environment around the urban stretch of the Porteiras stream in Petrolina, PE, and water quality by determining the Water Quality Index (WQI) and the Trophic State Index (TSI). Five visitation points and two water sampling points were defined in two sampling campaigns (dry and rainy periods). The influence of land use and occupation was evident in the WQI due to silting up, suppression of riparian vegetation, inadequate presence of waste and effluents, and in the TDI due to the contribution of nutrients from the discharge of domestic sewage and agricultural activity.

Varying stages of ecological succession in lakes subdivided by volcanic eruptions at Akan Caldera, Japan

Ecological succession within lakes generally proceeds as eutrophication and shallowing occur and the aquatic biota of the lakes is altered. The eutrophication rate depends on the lake size and the area and fertility of the watershed. If the watershed fertility of several different lakes is equivalent and the lakes’ formation time and initial environment are similar, the trophic status of each lake is expected to increase over time depending on the ratio of the watershed area to lake size. To test this supposition, we surveyed the topography and water quality of 10 lakes of varying sizes in Akan Caldera, Japan, which were formed thousands of years ago by fragmentation due to volcanic eruptions within the caldera. The ratio of the accumulated watershed area to lake size was positively correlated with total phosphorus concentration, an indicator of trophic status, and lake types were classified as oligotrophic, mesotrophic, eutrophic, and dystrophic. In addition, 21 species of macrophytes were found in the lakes, and the species composition of each lake was divided into five types corresponding to combinations of the lake types. The discovery of such diversity in a group of lakes with a similar origin paves the way for new comparative studies.

Long-term spatial-temporal monitoring of eutrophication in Lake Burdur using remote sensing data.

Lake eutrophication continues to be one of the major environmental challenges in lakes worldwide. This study is about using a remote sensing approach to monitor long-term chlorophyll-a (Chl-a) concentrations and the trophic state index (TSI) in Lake Burdur, Türkiye. Surface reflectance from Landsat 5, Landsat 7, and Landsat 8 satellite image collections were evaluated with an empirical equation to estimate a 38-year-long (1984-2021) time series of the lake's median Chl-a concentrations. Pixel quality masking was applied to retain only acceptable quality information and exclude images affected by cloud cover, icing, and other environmental factors from the analysis. The results were analyzed based on annual, seasonal, and monthly temporal averages. Over a period of 38 years, Chl-a concentrations were found to vary between 58.7 and 196.4 mg/m3. Notably higher concentrations were recorded in 2010 and 2021, while lower concentrations were observed between 1991 and 1993. A substantial increase in Chl-a concentration was evident from 2002 to 2010. The maximum concentration of Chl-a during the first two decades of the analysis was 130 mg/m3, which increased to 200 mg/m3 during the last two decades. Landsat-derived TSI values suggested that Lake Burdur has been mostly hypertrophic for the entire study period.

Seasonal variations in residence time and water age in the Mundaú-Manguaba Estuarine Lagoon System, AL (Brazil)

The Characteristic Hydraulic Times (CHT), called Residence Time (RT) and Water Age (WA), were analyzed in the Mundaú-Manguaba Estuarine Lagoon System (MMELS – AL, Brazil), using the SisBaHiA® – Environmental Hydrodynamics Base System, for two scenarios: wet season, from May to July 2018; and dry season, from October to December 2018. The hydrodynamic modelings appropriately represented water level variations measured in the lagoons. The analysis of residual currents revealed how hydrodynamic circulation was affected by seasonal variations, and provided essential information to understand the results of the RT and WA simulations. This study deepened the knowledge regarding the RT of the water masses inside the lagoons, and reinforced how river discharges significantly influence their export, which resulted, considering the spatial scope, in much smaller RT in the wet season compared to the dry season. The WA analysis added new and significant knowledge about water renewal, from a different perspective, and as yet little-explored in the study region. Among the results obtained, the most relevant refer to the dry season, in which it was found that the “oldest” waters in the Mundaú L. occurred near the southeast region, while in the Manguaba L., in the vicinity of the central region. Both regions were confirmed as the places that present the most critical trophic state index in each lagoon, showing that WA is a CHT that indicates the regions most conducive to more critical trophic states.&#x0D; Keywords: Mundaú-Manguaba lagoons, residence time, water age.

Assessment of the trophic state of the Soła River dam cascade, Polish Carpathians: a comparison of the methodology

The aim of this research was to determine the trophic state of mountain dam reservoirs, which are characterized by greater hydrological and ecological dynamics than lowland reservoirs. The trophic state of three dam reservoirs forming a cascade system was investigated. Trophic evaluation was carried out based on multiple criteria, i.e., (1) the content of chlorophyll a in the water, (2) planktonic algal biomass, (3) groups and species of algae, (4) the total phosphorus concentration in the water, and (5) the Integral Trophic State index (ITS). The analyzed parameters were characterized by high variability during the study period, which to a large extent may have resulted from the mountain environmental conditions. The greatest dynamics concerned parameters related to phytoplankton development. Unequivocal determinations of the trophic states of the reservoirs were difficult; however, it was found that in successive reservoirs of the cascade (from the highest to the lowest), a reduction in water fertility occurred.

Estimation of Water Carrying Capacity for Floating Net Cage Cultivation Activities in Pekalongan Coastal Waters

Floating cage fish farming is an aquaculture activity that is mostly carried out on the coast of Pekalongan. The purpose of this study was to estimate the carrying capacity of Pekalongan coastal waters as a floating net cage aquaculture activity zone. The research method used is descriptive qualitative and quantitative descriptive by calculating the indicators of Trophic Status Index (TSI), phosphorus, feed conversion ratio, and the carrying capacity level of the waters. The results showed that chlorophyll-a values ranged from 6.44-8.24 ꭒg/L, total phosphorus 12.44-14.80 ꭒg/L, feed conversion ratio 1.10-1.25, TSI (Trophic Status Index) values 48.2-54.6, harvested biomass 120-157 kg/ floating net cages (KJA). The carrying capacity of the waters for KJA cultivation is 145.43 tons of fish/year, and the number of existing KJA for cultivation is 110 KJA. The conclusion from the results of this study is that the carrying capacity on Pekalongan coastal waters when used as a floating net cage aquaculture activity zone is estimated to be able to accommodate approximately 145.43 tons of fish/year or the equivalent of 121 KJA. Currently, there are 110 KJA plots in the Jeruksari coastal waters, which means that the maximum carrying capacity of the waters that can be used for KJA cultivation is 11 KJA.

Determination of Quality and Trophic Status of Cibabat Lake, Cimahi City

In Cimahi City, the river water is heavily polluted, and well water is not suitable for drinking water, so to anticipate the lack of clean water, the Environmental Service is planning to revitalize one of the ponds, namely the Cibabat Lake. This study’s purpose is to determine the reservoir’s condition based on water quality and trophic status. The method used for calculating water quality status is the Pollutant Index, which refers to the Decree of the Minister of Environment Number 115 of 2003 with results is 8,450, and will be 8,751 in 2022, with the water quality classified status as moderately polluted. Meanwhile, the method to assess trophic status uses the Carlson Trophic State Index (TSI) method by taking air samples for the parameters Total Nitrogen, Total Phosphate, Chlorophyll-a, and brightness which is included in the hypereutrophic category. The Cibabat Reservoir has been polluted by domestic waste based on the calculation of the potential pollutant load such as BOD, COD, TSS, Total Phosphate and Total Nitrogen in the border area is 2,219,600; 3,051,950; 2,108,620; 11,623; and 108,206 kg/day, respectively. DTA area is 1,886.660: 2,594.158; 1,792.327; 9,905; 91.975 kg/day, respectively. This is influenced by the increasing population each year.

Trophic classification and assessment of lake health using indexing approach and geostatistical methods for sustainable management of water resources

Abstract This study aims to analyse the spatio-temporal trends in water quality, trophic state, and organic contamination of an alpine lake in the Darjeeling Himalaya through field investigations and to portray a comprehensive picture using multivariate analysis. Analysed water parameters have shown notable seasonal variations and were within the acceptable range for inland surface water. Water quality index (WQI) and organic pollution index (OPI) values have displayed ‘poor’ to ‘heavily polluted’ status in the pre-monsoon season, with marginally better conditions during the post-monsoon studies. Trophic state indices (TSIs) values revealed ‘eutrophic to highly eutrophic’ conditions during the investigation period. The results of the PCA have depicted three major determining factors (i.e., anthropogenic contribution, geogenic or weathering, and seasonal/climatic factors) that control the overall pollution level in the lake water system. The current study can potentially be a benchmark for assessing and undertaking management and restoration measures for this nascent alpine ecosystem.

Monsoon-induced response of algal chlorophyll to trophic state, light availability, and morphometry in 293 temperate reservoirs

Eutrophication management is one of the greatest environmental challenges for lacustrine systems worldwide. The empirically predicted models between algal chlorophyll (CHL-a) and total phosphorus (TP) provide a basis for managing eutrophication in lakes and reservoirs, but other environmental factors influencing the empirical relations must be considered. Here, we tested the impacts of morphological and chemical variables, as well as the effect of the Asian monsoon, on the functional response of CHL-a to TP using two-year data of 293 agricultural reservoirs. This study was based on the approaches of empirical models (linear and sigmoidal), CHL-a:TP ratio, and trophic state index deviation (TSID). Algal CHL-a exhibited a strong log-linear relation with TP on the basis of 2-year average data (R2 = 0.69, p < 0.001), whereas it had a more sigmoidal relation in terms of monsoon-seasonal averages (R2 = 0.52, p < 0.001). The linear segment of the CHL-a–TP relation aligned with the gradient of TP (10 mg/L < TP < 100 mg/L) from mesotrophic to eutrophic conditions. The transfer efficiency of TP to CHL-a based on the 2-year mean CHL-a:TP was high (0.6 <) across all assessed agricultural systems. CHL-a:TP showed insignificant correlations with reservoir morphological variations, but it decreased (<0.5) in eutrophic and hypereutrophic systems during the monsoon season (July–August). Because TP and total suspended solids (TSS) have become increasingly abundant, light conditions become insufficient for algal growth during and after the monsoon season. Light-limited conditions become more prevalent in hypereutrophic systems with shallow depth and high dynamic sediment ratio (DSR) because of the intense rainfall inputs and wind-induced sediment resuspension of the post-monsoon season. TSID reflected the degree of phosphorus limitation and the reduction in underwater light corresponding to changes in reservoir water chemistry (ionic content, TSS, and TN:TP ratio), trophic state gradient, and morphological metrics (mainly mean depth and DSR). Our findings suggest that monsoon-induced changes in water chemistry and light attenuation, which are also associated with anthropogenic pollutant runoffs and reservoir morphology, are critical factors that influence the functional response of algal CHL-a to TP in temperate reservoirs. Modeling and assessing eutrophication should therefore take into account monsoon seasonality along with individual morphological features further.

Dynamic Modeling of the Trophic Status of an Urban Tropical Wetland under ENSO Conditions

The climate variability associated with the ENSO phenomenon has a significant impact on wetlands, affecting the total precipitation input and hydrological flows of these ecosystems. The objective of this paper is to study the trophic status variation of an urban tropical wetland under ENSO conditions, through dynamic modeling. The results suggest an increase in precipitation, by 3.32 times, during the La Niña phase compared to the El Niño phase. Wetland input total phosphorus (TP) concentrations are 1.85 times lower during La Niña. This is probably due to a dilution effect exerted by the increase in surface runoff volumes from the basin. The findings suggest a reduction in wetland hydraulic retention time (HRT) during La Niña (1.33 times) compared to El Niño. This trend causes the TP concentration inside the wetland to decrease, possibly due to an increase in the water volume stored (dilution), and by the exit of this nutrient due to a shorter hydraulic renewal (HRT/La Niña &lt; HRT/El Niño). The occurrence of a high input of TP concentration to the wetland does not necessarily indicate a high trophic status index (TSI). This is because the trophic status of the wetland is possibly more associated with HRT rather than input TP concentration. The trophic status of the wetland during the La Niña tends to be eutrophic. Lastly, under ENSO scenarios, the use of Aizaki’s method is suggested, because it considers HRT as a decisive factor for the calculation of wetland trophic status.