Over the past half century, terrestrial nutrient discharge to freshwater ecosystems in Chinasignificantly increased with agriculture fertilization and climate warming. Simultaneously,severe eutrophication issues (algal bloom or high chlorophyll-a concentrations) werefrequently reported to occur in individual lakes based on satellite observations and in-situmeasurements in recent decades. Several measures to control point and non-point sources ofpollution were implemented to improve water quality in these lakes. However, unknowneutrophication status and the linkage between terrestrial nutrient exports and eutrophicationchanges on regional scales limited the proposal of effective measures for the control andimprovement of regional water quality. Furthermore, under sustainable development goals(SDGs) and markedly increased crop demand in the coming decades, it is necessary to attainhigher agriculture productivity while reducing environmental impacts. Although croplandreallocation has been proven as an effective measure to enhance agriculture production inChina, its potential contributions in reducing the environmental impacts under future climateconditions still have not been assessed.This thesis investigated the linkage between terrestrial nutrient sources and eutrophicationdynamics in regional lake ecosystems, and how to reduce future agricultural nitrogen exportswith crop production enhancement through optimizing crop spatial distributions in response tofuture climate changes. Firstly, regional eutrophication statuses and trends were assessed withthe probability of eutrophication occurrence (PEO) defined as satellite-derived algal bloomoccurrence or high chlorophyll-a concentrations (> 10 mg m-3) for the MERIS (2003-2011) andOLCI (2017-2018) observational periods. Secondly, terrestrial leached nitrogen simulated bya dynamic vegetation model LPJ-GUESS, together with agricultural phosphorus sources andindustrial wastewater discharge were used to represent terrestrial nutrient sources and examinetheir impacts on eutrophication changes from 2003 to 2011. Thirdly, crop spatial distributionsand fertilizer applications were optimized under future climate changes with three objectives(i.e., maximum of crop production, minimum of leached nitrogen and irrigation water use); andassociated leached nitrogen was then compared with that when maintaining current cropdistributions.Based on the MERIS (2003-2011) and OLCI (2017-2018) observations, algal blooms wereobserved to occur in totally seven lakes on the Yangtze Plain. High PEO values (> 50%, mostly >80%) dominated all fifty large lakes, where 21 out of 50 lakes experienced significantlydecreasing trends, while only one lake showed significantly increasing trends of PEO for theperiods of 2003-2018 (i.e., without 2012-2016 due to observational gaps between MERIS andOLCI). The leached nitrogen significantly increased with agriculture fertilization over theentire Yangtze Plain, with > 90% of contributions from agriculture ecosystems from 1979 to2018. Agriculture nutrient sources (i.e., leached nitrogen and total phosphorus sources) werepositively correlated with the PEO trends in the western and central regions from 2003 to 2011,while industrial wastewater discharge was strongly linked with the PEO changes in the easternlakes of the Yangtze Plain.The optimization of crop distributions reallocated the sown area of maize and rapeseed to rice,wheat, soybean, peanut, and potato, which results in reductions of leached nitrogen (0.97 ±0.56 Mt yr-1, or 14.2% ± 5.1%) and irrigation water use (22.3 ± 19.3 km3 yr-1, or 25.3% ±17.3%), as well as the increase of crop production (0.39 × 1015 ± 0.39 × 1015 kcal yr-1, or 18.8%± 19.3%) from 2020 to 2100. Such declining leached nitrogen also occurred in the drainagearea of fifty large lakes on the Yangtze Plain and 102 lakes with algal blooms on national scale.Our results showed the linkage between terrestrial nutrient sources and eutrophication trendson the Yangtze Plain, and the contributions of cropland reallocation in reducing futureagricultural nitrogen sources for lake ecosystems in China