Tributary Loadings and Their Impacts on Water Quality of Lake Xingyun, a Plateau Lake in Southwest China

Abstract

Lake Xingyun is a hypertrophic shallow lake on the Yunnan Plateau of China. Its water quality (WQ) has degraded severely during the past three decades with catchment development. To better understand the external nutrient loading impacts on WQ, we measured nutrient concentrations in the main tributaries during January 2010–April 2018 and modelled the monthly volume of all the tributaries for the same period. The results show annual inputs of total nitrogen (TN) had higher variability than total phosphorus (TP). The multi-year average load was 183.8 t/year for TN and 23.3 t/year for TP during 2010–2017. The average TN and TP loads for 2010–2017 were 36.6% higher and 63.8% lower, respectively, compared with observations in 1999. The seasonal patterns of TN and TP external loading showed some similarity, with the highest loading during the wet season and the lowest during the dry season. Loads in spring, summer, autumn, winter, and the wet season (May–October) accounted for 14.2%, 48.8%, 30.3%, 6.7%, and 84.9% of the annual TN load and 14.1%, 49.8%, 28.1%, 8%, and 84.0% of the annual TP load during 2010–2017. In-lake TN and TP concentrations followed a pattern similar to the external loading. The poor correlation between in-lake nutrient concentrations and tributary nutrient inputs at monthly and annual time scales suggests both external loading and internal loading were contributing to the lake eutrophication. Although effective lake restoration will require reducing nutrient losses from catchment agriculture, there may be a need to address a reduction of internal loads through sediment dredging or capping, geochemical engineering, or other effective measures. In addition, the method of producing monthly tributary inflows based on rainfall data in this paper might be useful for estimating runoff at other lakes.

Seasonal Water Quality Changes and the Eutrophication of Lake Yilong in Southwest China

“…The trophic level index (TLI), which reflecting lake trophic status [27] was used to evaluate the water quality of Lake Yilong. The aggregated TLI is calculated as the sum of individual TLIs, which are calculated according to lake and reservoir eutrophication evaluation methods and grading technical regulations, TN, TP, permanganate index (COD Mn ), DO, Chl-a, and Secchi disk transparency (SD) are the main indicators of nutrient levels in water [28,29]. Among them, the TLI is given as:…”

Nutrient loading from a sustainably certified aquaculture operation dwarfs annual nutrient inputs from a large multi-use watershed, Lake Yojoa, Honduras

“…Quantitative estimates of watershed scale loading of nutrients and quantified tributary contributions to lake ecosystems are rare in temperate zones and largely restricted to larger lakes (Robertson and Saad 2011, North et al 2013, Mooney et al 2020) and are even rarer in the tropics and subtropics (Coveney et al 2005, Li et al 2011, Luo et al 2022). Whereas many North American streams and rivers have been instrumented by the United States Geological Survey (USGS), no comparable effort to monitor discharge has yet to be broadly implemented for lower latitudes (Riveros-Iregui et al 2018).…”