Annual dynamics of water quality in a small urban landscape lake: a case study of Lake Wuzhou, China.

The aim of this study was to investigate the relationship between the water quality factors of Lake Wuzhou. This was achieved through an analysis of the annual dynamics of the water quality of Lake Wuzhou. This study also aimed at revealing the annual response mechanism of water factors, which not only includes the ecological theoretical significance, but also the extensive practical application potential for the management and evaluation of aquatic ecosystems in small water bodies. A total of 11 sampling points were chosen in Lake Wuzhou waters to collect sub-surface 2017, July 2017, September 2017 and November 2017 January 2018, and March 2018. After sample collection, pH, biochemical oxygen demand (BOD), chemical oxygen demand (COD), ammonia nitrogen (NH₃-N), total nitrogen (TN), total phosphorus (TP), nitrate-nitrogen (NO₃-N), and chlorophyll-a (Chl-a) were analyzed. The findings for the annual dynamics of water quality in Lake Wuzhou were as follows: (1) COD and BOD parameters were consistent except for those in March 2018 and May 2017 which were significantly lower than those for the other months; the annual dynamics findings for May 2017, September 2017 November, and January 2018 show an increasing trend. The results for TN and TP water quality parameters also show consistency for all the months except for those in January and March which are significantly lower than those in the other months. NH₃-N is significantly lower in March and September than those in the other months. The results for NO₃-N and Chl-a demonstrate high consistency for all the months except for those in November which were significantly higher than those in the other months while the results for May were significantly lower than those in other months. (2) BOD test measurements indicated that Lake Wuzhou water bodies are classified as class V water in the month of March 2018 and May 2017 but the results for BOD test measurements for all the other months indicated inferior class V water. The annual results for COD, NH₃-N, TN and TP of the water of Lake Wuzhou indicate an inferior class to class V water and this demonstrates that they are severely eutrophic water bodies. Carlson trophic state index was used to assess the nutritional status of water and the measurements led to the conclusion that Lake Wuzhou is severely eutrophic. (3) The correlation results of water quality factors of Lake Wuzhou waters were as follows: there is an extremely significant positive correlation between Chl-a and BOD, COD, TN, TP, NH₃-N, a significant negative correlation between pH and TN, TP, NO₃-N (p < 0.05), and an extremely significant negative correlation between NO₃-N and NH₃-N. In conclusion, Lake Wuzhou demonstrates a high presence of eutrophication which is driven by the accumulation of nutrients. To control the eutrophication, it is recommended that the density of reed communities should be increased while the density of lotus communities should be reduced. [ABSTRACT FROM AUTHOR]