Abstract
We studied the chemical water quality, physical habitat and biotic integrity of an urban stream subjected to restoration measures in South Korea. We used the water pollution index (WPI), qualitative habitat evaluation index (QHEI) and index of biotic integrity (IBI) on the water quality, physical habitat and fish assemblage data respectively, during 2007–2016 in Gap Stream to evaluate the ecological health before and after restoration measures. The results revealed annual mean total phosphorus (TP) dramatically decreased by 13-fold for 10 years and the values of biological oxygen demand (BOD) and chemical oxygen demand (COD) also decreased by >50% over the time, indicating decrease in nutrient enrichment and organic matter pollution after restoration measures. In the meantime, biological health analyses using IBI indicated no major transformation in fish assemblages under restoration impact. However, the proportion of sensitive species increased, and tolerant species decreased after restoration. Gap stream is home to 50 distinct fish species. QHEI proposed that the physical habitat health was in ‘good’ condition during the study period. WPI showed the chemical water quality status remained ‘poor’ during and before restoration but improved to ‘fair-good’ condition in the ensuing years after restoration. The IBI results, however, indicated ‘very poor-poor’ biotic integrity irrespective of restoration measures. CHL-a and TP showed strong (r < 0.7) to moderately strong (r = 0.5–0.7) correlation with significantly important water quality factors. Spatially significant pattern change in TN and TP was obvious as measured levels were significantly higher (p < 0.01) in downstream than upstream. Principal component analysis successfully indicated the placement of water quality factors and indices used as in three distinct stream compartments. The higher pollutant levels in the downstream mainly linked to the nutrient-rich effluents from emerging from the wastewater treatment plants (WWTPs) and industrial complexes operative in the stream catchment. Overall, restoration measures indicated minor impact on fish assemblages and physical habitat due to slow and steady improvement, however, water quality improved due to a decline of nutrients and chemicals downstream. This indicated a positive tendency of improvements in physical habitat and richness of fish assemblages in Gap Stream.
Highlights
The deteriorating ecological health of streams and rivers flowing through urban regions has become a significant research topic in freshwater ecology
We studied the ecological health of an urban stream subjected to restoration measures in terms of its chemical water quality, water pollution index (WPI), physical habitat health (QHEI) and biotic integrity (IBI)
The overall stream ecological health indicated that physical habitat, chemical water quality and biological integrity results indicated the inclusive effects of stream restoration measure were minor, chemical water quality as well as habitat health status upgraded slightly
Summary
The deteriorating ecological health of streams and rivers flowing through urban regions has become a significant research topic in freshwater ecology. The environmental degradation ensuing anthropogenic actions is instigating a progressive decline in regional aquatic biodiversity [4,5,6,7,8]. The leading cause of worsening aquatic environment is nutrient enrichment [9,10] and high organic matter loadings [11,12] originating from surface run-off and massive discharges of waste water treatment plants (WWTP) as well as industrial complexes [13]. In order to assess the success of restoration measures in terms of water quality, several chemical approaches have been frequently used for the assessment of contaminants in aquatic environments because of cost-effectiveness and the ease of estimating the degree of pollution [16]. Some problems and the ambiguity of the chemical measurements such as high spatial variation (microhabitat changes) and temporal variations (diel changes) were pointed out in other researches [18,22]
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