Decoding the interactive effect of water quality-land use on benthic macroinvertebrate biodiversity in rivers with an interpretable machine learning framework

BackgroundDisentangling the relative importance of environmental variables and interspecific interaction in modulating co-occurrence patterns of sympatric species is essential for understanding the mechanisms of community assembly and biodiversity. For the two sympatric Galliformes, Silver Pheasants (Lophura nycthemera) and White-necklaced Partridges (Arborophila gingica), we know little about the role of habitat use and interspecific interactions in modulating their coexistence.MethodsWe adopted a probabilistic approach incorporating habitat preference and interspecific interaction using occupancy model to account for imperfect detection, and used daily activity pattern analysis to investigate the co-occurrence pattern of these two sympatric Galliformes in wet and dry seasons.ResultsWe found that the detection probability of Silver Pheasant and White-necklaced Partridge were related to habitat variables and interspecific interaction. The presence of Silver Pheasant increases the detection probability of White-necklaced Partridge in both the wet and dry season. However, the presence of White-necklaced Partridges increases the detection probability of Silver Pheasants in the wet season, but decreases the probability in the dry season. Further, Silver Pheasants were detected frequently in the sites of high values of enhanced vegetable index (EVI) in both the wet and dry season, and in sites away from human residential settlement in the wet season. White-necklaced partridges were mainly detected in low EVI sites. The site use probabilities of two Galliformes were best explained by habitat variables, Silver Pheasants and White-necklaced Partridges preferred steeper areas during the wet and dry season. Both species mainly occurred in low EVI areas during the wet season and occupied sites away from the resident settlement during the dry season. Moreover, the site use probabilities of two species had opposite relationships with forest canopy coverage. Silver Pheasants preferred areas with high forest canopy coverage whereas White-necklaced Partridges preferred low forest canopy coverage in the dry season, and vice versa in the wet season. Species interaction factor (SIF) corroborated weak evidence of the dependence of the site use of one species on that of the other in the either dry or wet season. Temporally, high overlapping of daily activity pattern indicated no significantly temporal niche differentiation between sympatric Galliformes in both wet and dry seasons.ConclusionsOur results demonstrated that the presence of two species influenced the detection probability interactively and there was no temporal partitioning in activity time between Silver Pheasants and White-necklaced Partridges in the wet and dry seasons. The site use probability of two Galliformes was best explained by habitat variables, especially the forest canopy coverage. Therefore, environmental variables and interspecific interaction are the leading drivers regulating the detection and site use probability and promoting co-occurrence of Silver Pheasants and White-necklaced Partridges.

As an important part of the riverine carbon cycle, dissolved inorganic carbon (DIC) has attracted continuous attention. The stable carbon isotope (δ13CDIC) of DIC can reflect its sources and transformations. However, the effects of land use on DIC and δ13CDIC are rarely investigated. To study the influencing factors of DIC and δ13CDIC, river water samples were collected and analyzed from the Chishui River basin, a typical karst river basin in southwestern China. The upper reaches of the Chishui River basin were predominantly underlain by carbonate sedimentary rocks, whereas the lower reaches contained mostly siliciclastic sedimentary rocks, and the forest coverage in the lower reaches was relatively high. The elemental compositions of the river water revealed that the hydrochemistry of rivers in the upper reaches of the basin was mainly controlled by carbonate weathering, whereas the hydrochemistry of some tributaries in the lower reaches was mainly affected by silicate weathering. During the wet season, the average values of c (DIC) and the δ13CDIC value were (1940±493) μmol·L-1 and (-9±1) ‰, respectively, whereas the c (DIC) was relatively high, and the δ13CDIC value was more positive in the dry season, with the average values of (2334±626) μmol·L-1 and (-7.3±1) ‰, respectively. The DIC of most samples was mainly controlled by carbonate weathering under an open system and was derived from carbonate minerals and atmospheric and soil CO2. The seasonal variations in the c (DIC) and δ13CDIC values suggested that c (DIC) was regulated by climate, hydrology, and biology. The increasing contribution of biological carbon to DIC in summer was the main cause of the more negative δ13CDIC value in the wet season, whereas the dilution effect of higher discharge was the main cause of the low c (DIC) in the wet season. The samples from three tributaries in the lower reaches with the highest proportion of silicate and forest distribution had the highest dissolved organic carbon concentration[c (DOC)], the lowest c (DIC), and the most negative δ13CDIC value in the wet season. The proportion of carbonate distribution had positive correlations with c (DIC) in the wet and dry seasons, indicating that lithology was the main controlling factor of c (DIC). The rivers draining the carbonate areas had a lower c (DIC) and a more negative δ13CDIC value in the wet season than those in the dry season, whereas for the rivers draining non-carbonate areas with high forest coverage, the c (DIC) was higher and the δ13CDIC value was significantly more negative in the wet season than those in the dry season. This implies that c (DIC) and δ13CDIC are significantly affected by land use when they are less affected by lithology.

Land use, hydrology, and climate influence water quality of China's largest river

The coupling between land use/landscape pattern and water quality in river systems varies across different spatial and temporal scales. It is important to understand the association between water quality and land use/landscape pattern across different spatial and temporal scales for the protection of water resources. Here, we measured seasonal water quality at 12 sub‐basins in the upper reaches of the Han River (UHR) between 2010 and 2018. We conducted factor analysis and redundancy analysis to determine the links between land use and water quality at multiple spatial scales and to identify the main factors influencing water quality. We found that the concentration of nutrients, including total nitrogen, total phosphorus, nitrate‐N and ammonium‐N, was higher during the wet season than the dry season. Total nitrogen was the main driver of nutrient pollution in the UHR, whereas total phosphorus was identified as another potential nutrient pollutant. We also found that water quality parameters were more strongly related to land use types during the wet season than the dry season. Croplands and urban lands increased phosphorus concentrations of river water, whereas forest and grasslands decreased the nitrogen concentrations of river water at the sub‐basin scale. Land use at the riparian zone scales better explained variations in water quality than land use at sub‐basin scales. The explained variations in landscape metrics were generally higher during the dry season than the wet season. The largest patch index and Shannon's diversity index were the main predictors of river water quality in the UHR.

Island ecosystems often have a disproportionate number of endemic species and unique and fragile functional characteristics. However, few examples of this type of ecosystem have been reported. We conducted a comprehensive field study on Neilingding Island, southern China. The leaf samples of 79 subtropical forest tree species were obtained and their functional traits were studied in the dry and wet seasons to explain the relationships between plant functional traits and soil nutrients. We found a greater availability of soil moisture content (SMC) and nutrients in the wet season than in the dry season. The values of wet season soil available phosphorus (5.97 mg·kg-1), SMC (17.67%), and soil available potassium (SAK, 266.96 mg·kg-1) were significantly higher than those of the dry season. The leaf dry matter content, specific leaf weight, leaf density, leaf total carbon, leaf total nitrogen, leaf total calcium, and the N/P and C/P ratios of leaves were all significantly higher in the dry season than in the wet season, being 18.06%, 12.90%, 12.00%, 0.17%, 3.41%, 9.02%, 26.80%, and 24.14% higher, respectively. In contrast, the leaf area (51.01 cm2), specific leaf area (152.76 cm2·g-1), leaf water content (0.59%), leaf total nitrogen (1.31%), leaf total phosphorus (0.14%), and leaf total magnesium (0.33%) were much lower in the dry season than in the wet one. There were significant pairwise correlations between leaf functional traits, but the number and strength of correlations were significantly different in the dry and wet seasons. The SAK, soil total phosphorus (STP), and pH impacted plant leaf functional traits in the dry season, whereas in the wet season, they were affected by SAK, STP, pH, and NO3- (nitrate). Both soil nutrients and water availability varied seasonally and could cause variation in a number of leaf traits.

A systematic data analytics was employed to determine the relative linkages of stream water quality and environmental health with the land use and hydrologic drivers in the coastal‐urban watersheds of southeast Florida. Power law‐based partial least squares regression models were developed to reliably estimate the linkages by appropriately resolving multicollinearity (Nash‐Sutcliffe efficiency = 0.72–0.95). The analytics indicated Everglades as the external and the largest source of total nitrogen (TN) in the coastal‐urban streams for both wet (June–October) and dry (November–May) seasons. The “external driver” exhibited 1.5–2 times stronger control on stream TN than that of the watershed “land use,” “hydrology,” and the “upstream reach” contributions. In contrast, Everglades appeared to be a minor source of in‐stream total phosphorus (TP), which was predominantly controlled by the internal watershed processes. TP was most strongly linked with the upstream reach concentrations and watershed land uses in the wet and dry seasons, respectively. Despite the predominantly built‐up fraction (74%) of the study area, agricultural land was the most substantial watershed source of in‐stream nutrients. The linkages of algal biomass (Chl a) with the drivers indicated TP as the limiting nutrient. Stream dissolved oxygen was most strongly influenced by the adjacent groundwater depth and watershed land uses, respectively, in the wet and dry seasons. The estimated relative linkages and insights would be useful to identify the management targets and priorities to achieve healthy coastal‐urban stream ecosystems in southeast Florida and around the world.

Effects of land use on water quality in a River Basin (Daning) of the Three Gorges Reservoir Area, China: Watershed versus riparian zone

Landscape patterns can affect the biogeochemical cycles of river ecosystems. The Danjiang River Basin is an important water source for the central line project of the South-to-North Water Diversion. Investigating the influence of landscape patterns on runoff dissolved organic matter (DOM) is of great significance for the ecological protection of the basin. Based on field sampling data collected during the normal season (November 2023), dry season (March 2024), and wet season (July 2024), this study analyzed the spatial-temporal variation characteristics of runoff DOM in the Danjiang River Basin using excitation-emission matrix-parallel factor analysis (EEM-PARAFAC). The impacts of landscape patterns and hydrochemistry on dissolved organic matter (DOM) were assessed using the random forest model, redundancy analysis (RDA), and variance partitioning analysis (VPA). The results showed that the average concentration of dissolved organic carbon (DOC) in runoff in the Danjiang River Basin was 5.03 mg·L-1, with a variation range of 2.59-9.96 mg·L-1. The DOC concentration was highest during the wet season (5.80 mg·L-1), followed by that during the dry season (5.28 mg·L-1), and lowest during the normal season (4.02 mg·L-1). Humic-like DOM accounted for 67.07% and 79.45% of the DOM during the normal and wet seasons, respectively. During the dry season, the relative abundances of humic-like and protein-like DOM were 49.21% and 50.79%, respectively. During the wet and normal seasons, dissolved organic matter (DOM) in the water exhibited stronger exogenous characteristics, while during the dry season, DOM showed more pronounced autochthonous characteristics. The spatial and temporal scales with the strongest influence of landscape pattern on DOC concentration and DOM composition were the 500 m circular buffer during the dry season and the 200 m circular buffer during the wet season, respectively. Urban land, ammonia nitrogen, and landscape patch cohesion index were the main factors driving the change in DOC. Water temperature, electrical conductivity, and total phosphorus (hydrochemistry factors), as well as forest land, grassland, and cropland (land use types), were significant influencing factors on the variation of runoff DOM components in the Danjiang River Basin. Additionally, the aggregation index and continuity index (landscape configuration metrics) also played important roles. These findings can provide reliable data for rational land use planning and serve as a reference for water environment management in the Danjiang River Basin.

Comparison of water level and eutrophication indicators during the wet and dry period in a eutrophic urban lake

BackgroundThe application of index of biotic integrity (IBI) to evaluate river health can be an essential method for river ecosystem management. However, these types of methods were developed in small, low-order streams, and are therefore, infrequently applied to large rivers. To that end, phytoplankton communities and environmental variables were monitored in 30 sampling segments of the middle and lower reaches of the Yangtze River, China during the wet (July–August) and dry (November–December) seasons in 2017–2018. We developed a phytoplankton-based index of biotic integrity (P-IBI) and used the index to assess the ecological health of the Yangtze River. Relationships among P-IBI, its component metrics, and environmental factors were analyzed across different seasons.ResultsResults obtained from the P-IBI indicated that the phytoplankton-based ecological health of the Yangtze River was rated as “good” during both seasons, with an overall better condition in the dry season. During the wet season, there were scattered river segments with P-IBI ratings of “fair” or below. Water quality and land use appeared to shape the patterns of P-IBI. In the wet season, P-IBI negatively correlated with total phosphorus, nitrate, total suspended solids, turbidity, conductivity, and dissolved oxygen. In the dry season, P-IBI positively correlated with total nitrogen, ammonium, and nitrite, and negatively correlated with water temperature.ConclusionsThe ecological health of the Yangtze River as reflected by the P-IBI exhibited spatial and temporal variability, with the effect of water quality being greater than that of local land use. This study indicated the importance of considering seasonal effects in detecting large river ecological health. These findings enhanced our understanding of the ecological health and characterized potential benchmarks for management of the Yangtze River. These findings also may be applicable to other large rivers elsewhere.

Impacts of land uses on spatio-temporal variations of seasonal water quality in a regulated river basin, Huai River, China

The Chi and Mun River Basins, the primary tributary of the Mekong River Basin in Thailand, is undergoing significant land use changes that impact water quality. Understanding the relationship between land use and water quality is crucial for effective river basin management, providing insights applicable to global water systems. While past studies have examined water quality in the Mekong River Basin, research specifically focusing on the Chi-Mun River Basin remains limited. This study analyzes the spatial and temporal effects of land use changes on water quality from 2007 to 2021 using land use change estimation, 11 water quality parameters, and redundancy analysis (RDA). Water samples were collected in January, March, May, and August across multiple years. Seasonal variations were assessed, with dry season samples from January and March and wet season samples from May and August. Key findings include: (1) pH, Biochemical Oxygen Demand, Total Coliform Bacteria, Fecal Coliform Bacteria, Total Phosphorus, Nitrate Nitrogen, Ammonia-Nitrogen, and Suspended Solids increased during the wet season, while (2) Dissolved Oxygen, Electrical Conductivity, and Water Quality Index were higher in the dry season. (3) Land use changes had a greater impact on water quality during the wet season, driven by increased runoff from expanding urban and agricultural areas and declining paddy and forest cover. (4) Forests and aquatic areas improved water quality, while agricultural and urban expansion contributed to its deterioration. These findings underscore the need for sustainable land management strategies to balance regional development with ecological conservation in the Chi-Mun River Basin.

Factors influencing the spatio-temporal dynamics of plankton communities in small tropical lakes are not well-understood. This study assessed plankton communities in response to spatial (six sampling sites) and seasonal (wet vs. dry seasons) changes in environmental variables in Lake Kanyaboli, a small satellite lake on the northern shores of Lake Victoria, Kenya. Water quality variables, including pH, conductivity (EC), dissolved oxygen (DO), temperature, Secchi depth (SD), nitrates (NO3-), nitrites (NO2-), ammonium (NH4+), soluble reactive phosphorus (SRP), total nitrogen (TN), total phosphorus (TP), and chlorophyll-a(Chl-a), were monitored monthly at six sites spread throughout the lake for 1 year. Phytoplankton and zooplankton samples were collected and analyzed for taxon composition and abundance. Two-way ANOVA showed no significant interaction between site and season for all variables. Likewise, there were no significant spatial differences for all variables except Chl-a. At-test showed significant seasonal differences in SD, DO,NH4+,NO3-,NO2-, and TN. Thirty phytoplankton genera were identified belonging to Bacillariophyceae, Chlorophyceae, Cryptophyceae, Cyanophyceae, Euglenoidae, Trebouxiophyceae, and Zygnematophyceae, with Chlorophyceae being the most dominant (42.30%). Zooplankton comprised of 15 genera, belonging to Copepoda (55.4%), Rotifera (27.9%), and Cladocera (16.7%). Two-way ANOVA for plankton abundance showed no significant interaction between site and season, but there were significant differences in community composition between the wet and dry seasons. Canonical correspondence analysis identified water clarity (Secchi depth) and concentrations of dissolved fractions of nitrogen and phosphorus as the major water quality variables driving variation in the composition of plankton communities in the lake. This study showed that seasonality was a major driver of changes in plankton community composition between dry and wet seasons through changes in the concentrations of nutrients (NH4+,NO3-,NO2-, TN, and TP). Lake Kanyaboli's phytoplankton community indicated a non-equilibrial state, perhaps due to short residence times of water, especially during the wet season, and dense macrophytes fringing the lake that increase nutrient uptake and limit the dominance of select phytoplankton species. This study shows the importance of long-term studies covering dry and wet seasons to understand the dynamics of plankton communities and their drivers in small tropical waterbodies to inform management and conservation.

Biotic and abiotic properties most closely associated with subtropical forest soil respiration differ in wet and dry seasons: A 10-year in situ study

The aim of the study was to evaluate the effects of coniferous forest cover in the catchment basin and relative catchment area (catchment area to lake volume ratio) on phytoplankton composition in humic lakes. The study was carried out in 11 small and shallow lakes situated in the West Polesie region (Eastern Poland). The lakes were divided with respect to forest cover in their catchment basins into two groups: high forest cover — HFC (more than 60%) and low forest cover — LFC (less than 60%). The study showed that both, land use in the catchments (proportion of forests) and the relative catchment area determined physicochemical and biological parameters in the lakes. The high relative catchment area affects their high productivity expressed by high chlorophyll a concentration and low water visibility. The lakes of the LFC group had low water colour as well as high concentration of total phosphorus (Ptot), reaction (pH), and conductivity of water and a large number of cyanophytes and chlorophytes. The dominant species, e.g., Planktolyngbya limnetica, Limnothrix planctonica, Planktothrix agardhii, Coenococcus planctonicus, were characteristic of high trophic status. In the lakes of the HFC group, Ptot, pH, conductivity of water and the contribution of cyanophytes and chlorophytes was considerably lower, whereas the water colour and the number of raphidophytes represented by Gonyostomum semen was high. The large number of raphidophytes and the small amount of chlorophytes and cyanophytes in the lakes of the HFC group indicated the lake naturalness.