Ecological River Health Assessment Using Multi-Metric Models in an Asian Temperate Region with Land Use/Land Cover as the Primary Factor Regulating Nutrients, Organic Matter, and Fish Composition

Abstract

This study was performed to determine the ecological health of a temperate river over nine years (2011−2019); it also analyzed the trophic structure and linkage of nutrients (nitrogen [N] and phosphorus [P]), sestonic chlorophyll-a (CHL-a), and the top trophic fish in the Asian monsoon region. Water chemistry, trophic indicators, and tolerance guilds were primarily influenced by land use and land cover (LULC); the magnitude of variation was also related to geographic elevation, artificial physical barriers (weirs), and point sources. Levels of nutrients, organic matter, and CHL-a largely influenced by the intensity of the monsoon seasonality for a particular LULC and stream order. Mann−Kendall tests based on a long-term annual dataset showed that annual organic matter and CHL-a increased over time because of longer hydraulic residence time after weir construction. The results of empirical nutrient models suggested that P was the key determinant for algal growth (CHL-a); the strong P-limitation was supported by N:P ratios > 17 in ambient waters. Linear regression models and canonical correspondence analysis (CCA) were used to determine the influences of LULC and water quality on the trophic/tolerance linkages, fish community compositions and structures, and river health. Tolerant species had a positive functional relationship with nutrient enrichment through total phosphorus (TP) (R2 = 0.55, p < 0.05) and total nitrogen (TN) (R2 = 0.57, p < 0.05), organic pollution in terms of biological oxygen demand (BOD) (R2 = 0.41, p < 0.05) and chemical oxygen demand (COD) (R2 = 0.49, p < 0.05), and algal growth (R2 = 0.47, p < 0.05); sensitive species exhibited the opposite pattern. The degradation of river health, based on the multi-metric index of biotic integrity (IBI) model, was evident in the downriver region (“fair−poor” condition) and was supported by the quantitative fish community index (QFCI) model. The outcomes suggested that the degradation and variation of ecological river health, trophic linkages of water chemistry (N, P)-algal biomass-fish, were largely controlled by the land use pattern and construction of physical barriers in relation to the Asian monsoon.

Keywords: Asian monsoon; fish indicator; multi-metric fish model; nutrient enrichment; river health.

Figure 1

Map showing the sampling sites in the mainstream of the Geum River. SW, Sejong Weir; GW, Gongju Weir; BW, Baekje Weir; WWTP, wastewater treatment plant.

Figure 2

Site variations of water quality parameters in the Geum River basin (TP, total phosphorus; TN, total nitrogen; BOD, biological oxygen demand; COD, chemical oxygen demand; TSS, total suspended solids; CHL-a, chlorophyll-a. The red dots indicate the mean value, the first highest mean receives the letter “a”, the second, third, fourth, and fifth highest mean receives the letter “b”, “c”, “d” and “e”, respectively, and means with no significant difference receive the same letter).

Figure 3

Relationships of LULC with water quality variables (AGC, agricultural coverage; BUA, built-up area coverage; FOC, forest coverage; TP, total phosphorus; TN, total nitrogen; BOD, biological oxygen demand; COD, chemical oxygen demand).

Figure 4

Relations of algal chlorophyll (CHL-a) with total nitrogen (TN) and total phosphorus (TP) in the Geum River before weir construction (WCs) and after the weir construction.

Figure 5

Chemical and biological health status of the Geum River basin based on sites and year (red bars indicate “poor” and “very poor” condition).

Figure 6

Relations among the Index of Biotic Integrity (IBI) and Quantitative Fish Community Index (QFCI) model values with tolerant and trophic guild.

Figure 7

Canonical correspondence analysis (CCA) ordination diagram of trophic and tolerance guilds with water quality variables and land-use pattern and elevation. IS, intermediate species; SS, sensitive species; TS, tolerant species; C, carnivore; I, Insectivores; O, omnivores; AG, agricultural land-use coverage; FOR, forest land-use coverage; BUA, built-up area; WT, water temperature; BOD, biological oxygen demand; COD, chemical oxygen demand; TSS, total suspended solids; TP, total phosphorus; TN, total nitrogen; CHL-a, chlorophyll-a; EC, electrical conductivity.