Can the establishment of a protected area improve the lacustrine environment? A case study of Lake Chaohu, China.

Eutrophication of lacustrine environments with frequent cyanobacterial blooms has become a serious problem. Overpopulation and runoff into groundwater and lakes from fertilizers with too much nitrogen and phosphorous have caused most of the problems. Here, we first devised a land use and cover classification system based on the local characteristics of the first-level protected area of Lake Chaohu (FPALC). Lake Chaohu is the fifth largest freshwater lake in China. The land use and cover change (LUCC) products were produced using sub-meter resolution satellite data from 2019 to 2021 in the FPALC. This study presents an evaluation of the effectiveness of the established protected areas. The results show the most impactful type was the reduction in cropland with an area that declined from 7446.4 hm2 to 6433.3 hm2 from 2019 to 2021. Most of the reduced cropland was converted into wetlands, with 460.2 hm2 and 152.0 hm2 of cropland restored to wetlands from 2019 to 2020 and 2020-2021, respectively. The area of cyanobacterial blooms in Lake Chaohu showed a downward trend, and the lacustrine environment was greatly improved after the establishment of the FPALC. These quantified data can inform decision-making related to Lake Chaohu conservation and provide a reference for managing the aquatic environment in other watersheds.

Controls for multi-temporal patterns of riverine nitrogen and phosphorus export to lake: Implications for catchment management by high-frequency observations.

Intensifying human activity coupled with climate change increase the transport of excess riverine nitrogen (N) and phosphorus (P) loading from catchment to lake, leading to eutrophication and harmful algal blooms worldwide. To improve understanding of multi-temporal patterns of riverine N and P export and their hydro-biogeochemical controls over both episodic events and long-term trend, we analyzed and interpreted high-frequency data of total nitrogen (TN), ammonia-nitrogen (NH4-N), and total phosphorus (TP) provided by an automatic water quality monitoring station in a typical agricultural catchment draining to Lake Chaohu, China. Mann-Kendall test revealed a significant decreasing trend of riverine N and P concentration most of the time during 2018-2020. At the sub-daily scale, intraday TN concentrations varied by more than 1 mg/L in 31.8% of the period. Monthly TN and TP concentrations were particularly high in December 2019, indicating combined effect of hydrologic (long dry antecedent period and subsequent intensive rainfall events) and anthropogenic controls (fertilization and agricultural drainage). Significantly higher TN concentrations in winter and TP concentrations in summer reflected coupled dominances of precipitation and temperature on hydrologic and biogeochemical processes. Rainfall events with very heavy intensity drove disproportionate N and P loads (more than 20% of the total export) in only 3.2% of the period. Moderate and very heavy events registered the highest TN and TP concentrations, respectively. Our results highlighted the importance of automatic water quality monitoring station to reveal dynamics of riverine N and P export, which may imply future nutrient loading abatement plans for lake-connected catchment.

Rapid expansion of coastal aquaculture ponds in Southeast Asia: Patterns, drivers and impacts.

Aquaculture pond is one of the most important land use types and a main income source in coastal zones in Southeast Asia. However, the fast expansion of aquaculture ponds threatens coastal ecosystems - an issue that Sustainable Development Goals (SDGs)14 seeks to address. Investigating expansion patterns is essential for exploring the drivers and understanding its impacts, and thus the focus of the sustainable management of aquaculture. This study aims to assess the spatio-temporal expansion patterns of aquaculture ponds with multitemporal remote sensing images and geographic information system in the coastal zone of Southeast Asia over a 25-year period (1990-2015), to understanding how globalization and economic policies may have contributed to such changes. The results show that, in 2015, total area of coastal aquaculture ponds was about 23,245 km2, and 79% of coastal aquaculture ponds distributed within 15 km from the coastline. And the amount has expanded about 2.6 times in the past 25 years. Vietnam has the largest area of aquaculture in 2015 and the highest annual increasing rate, accounting for 40.28% and 298.5 km2/y, followed by Indonesia (31.50% and 156.8 km2/y), Thailand (10.79% and 64.8 km2/y), Myanmar (8.76% and 61.1 km2/y). The expansion pattern of aquaculture ponds in the region altered from outlying to edge-expansion from the year of 2000. The main drivers of rapid expansion lie to the intensified local fisher policies as a result of economic globalization. While development of aquaculture has enhanced family income, it has also led to significant reduction of mangrove and coastal water pollution (eutrophication). With the prevailing antagonism between aquaculture expansion and ecosystem conversion, our research call for the local government's attention to sustainable management of aquaculture. This will be the key to reduce food safety risk and simultaneously prevent inevitable damages to coastal ecosystems, as stipulated by SDGs 2 and 14.