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Abstract:Understanding the relationship between land use and surface water quality is necessary for effective water management. We estimated the impacts of catchment-wide land use on water quality during the dry and rainy seasons in the Dongjiang River basin, using remote sensing, geographic information systems and multivariate statistical techniques. The results showed that the 83 sites can be divided into three groups representing different land use types: forest, agriculture and urban. Water quality parameters exhibited significant variations between the urban-dominated and forest-dominated sites. The proportion of forested land was positively associated with dissolved oxygen concentration but negatively associated with water temperature, electrical conductivity, permanganate index, total phosphorus, total nitrogen, ammonia nitrogen, nitrate nitrogen and chlorophyll-a. The proportion of urban land was strongly positively associated with total nitrogen and ammonia nitrogen concentrations. Forested and urban land use had stronger impacts on water quality in the dry season than in the rainy OPEN ACCESSWater 2015, 7 4428 season. However, agricultural land use did not have a significant impact on water quality. Our study indicates that urban land use was the key factor affecting water quality change, and limiting point-source waste discharge in urban areas during the dry season would be critical for improving water quality in the study area.

The aim of this study was to assess the impacts of different land use practices on physicochemical characteristics and macroinvertebrate functional feeding groups (FFGs) in the Dongjiang River basin, southeast China and also to evaluate if macroinvertebrate FFGs match the river continuum concept (RCC) predictions. For this aim, a total of 30 sampling sites were selected that comprised three different land use types (10 forest, 10 agricultural, and 10 urban sites) and sampled during the dry season in January 2013. Analysis of variance results showed evident differences in the environmental factors among the three land use types, particularly between the forest and urban sites. The forest sites had significantly lower water temperature, lower stream order, higher pH, higher dissolved oxygen, higher elevation, and coarser substrates than the other land use sites. Conversely, the urban sites showed significantly higher mean values for electrical conductivity, nitrogen and phosphorus compounds. Significant differences in the shredder and predator richness and density were observed among land uses with more shredders and predators found in forest sites. Redundancy analysis showed a clear separation of forest sites from riparian modified areas (agriculture and urban use sites). Our results were broadly in accordance with the central RCC theme. However, the longitudinal distribution of predators and collectors did not completely match the prediction of the RCC. These results confirm that macroinvertebrate FFG structure has been altered by agricultural and urbanization practices in the Dongjiang River basin. Moreover, shredders and predators could be potential candidates for monitoring and assessing land use impacts on water quality in this basin to improve future watershed management.

The dissolved organic matter (DOM) composition in river ecosystems could reflect the human impacts on the river ecosystem, and plays an important role in the carbon cycling process. We collected water and phytoplankton samples at 107 sites in the Dongjiang River in two seasons to assess the impact of the sub-catchments land use structure on the DOM composition. The results showed that (1) the forested subcatchments had higher humic-like C1 (16.45%) and C2 (25.04%) and lower proteinlike C3 (22.57%) and C4 (35.95%) than urbanized and mixed forest-agriculture subcatchments, while the urbanized sub-catchments showed an inverse trend (4.54%, 15.51%, 33.97% and 45.98%, respectively). (2) The significant variation in the proportion of C1 and C4 between the dry and rainy seasons was recorded in both the forested and the mixed forest-agriculture sub-catchments (p<0.01), but only C4 showed an obvious seasonal variation in the urbanized sub-catchments (p<0.01). While the DOM composition was mainly related to the proportion of urbanized land and forested land year-round (p<0.01), it had stronger correlation with forested land in the dry season and urbanized land in the rainy season.(3) No significant correlation between the DOM composition and the agricultural land proportion was found in either season (p>0.05).Our findings indicated that the DOM composition was strongly dependent on the land use structure of the sub-catchments and varied seasonally, but the seasonal variation pattern could be disturbed by human activities in the extensively urbanized catchments.Notably, the higher C4 proportion compared with those in temperate rivers implied a larger amount of CO2 released from the subtropical rivers into the atmosphere when considering bioavailability.

Abstract:The phytoplankton community in the river is closely related to the location of the river and the impact of human activities. To summarize the patterns of phytoplankton community changes in rivers and to analyze the reasons for these patterns and differences, we sampled the three tributaries of the Dongjiang River at different latitudes in the dry and rainy season for three years. The results showed that the three rivers were mesotrophic, lightly eutrophic and moderately eutrophic respectively. From the south to the north, the water temperature and nutrition showed an increasing trend. In two different seasons, the differences in the water temperature and dissolved oxygen were clear. In the dry season, results of the multidimensional scaling (MDS) analysis indicated that the phytoplankton community structures in the Li River and Qiuxiang River were similar. Regardless of the number of species, the cell abundance or the dominance index, Bacillariophyta were found to be dominant. Chlorophyta was dominant in the Danshui River. In the rainy season, Bacillariophyta, Bacillariophyta-Chlorophyta and Chlorophyta-Cyanophyta became the dominant types in the Li River, Qiuxiang River and Danshui River, respectively. These different patterns in phytoplankton community variation were affected by both the water quality and temperature.