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Assessing the impacts of environmental change and anthropogenic activities on the historical and current total suspended matter (TSM) pattern in Dongting Lake, China, is a large challenge. We addressed this challenge by using more than three decades of Landsat data. Based on in situ measurements, we developed an algorithm based on the near-infrared (NIR) band to estimate TSM in Dongting Lake. The algorithm was applied to Landsat images to derive TSM distribution maps from 1978 to 2013 in the wet season, revealing significant inter-annual and spatial variability. The relationship of TSM to water level, precipitation, and wind speed was analyzed, and we found that: (1) sand mining areas usually coincide with regions that have high TSM levels in Dongting Lake; (2) water level and seven-day precipitation were both important to TSM variation, but no significant relationship was found between TSM and wind speed or other meteorological data; (3) the increased level of sand mining in response to rapid economic growth has deeply influenced the TSM pattern since 2000 due to the resuspension of sediment; and (4) TSM variation might OPEN ACCESSRemote Sens. 2015, 7 13976 be associated with policy changes regarding the management of sand mining; it might also be affected by lower water levels caused by the impoundment of the Three Gorges Dam since 2000.

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Chlorophyll-a (Chla) is an important indicator of water quality and eutrophication status. Monitoring Chla concentration (C ) and understanding the interactions between C and related environmental factors (hydrological and meteorological conditions, nutrients enrichment, etc.) are necessary for assessing and managing water quality and eutrophication. An acceptable Landsat 8 OLI-based empirical algorithm for C has been developed and validated, with a mean absolute percentage error of 14.05% and a root mean square error of 1.10 μg L. A time series of remotely estimated C was developed from 2013 to 2015 and examined the relationship of C to inflow rate, rainfall, temperature, and sunshine duration. Spatially, C values in the riverine zone were higher than in the transition and lacustrine zones. Temporally, mean C value were ranked as spring> summer > autumn > winter. A significant positive correlation [Pearson correlation coefficient (r) = 0.88, p < 0.001] was observed between the inflow rate and mean C in the northwest segment of the Xin'anjiang Reservoir. However, no significant relation was observed between mean C and meteorological conditions. Mean (± standard deviation) value for the ratio of total nitrogen concentration to total phosphorus concentration in our in situ dataset is 75.75 ± 55.72. This result supports that phosphorus is the restrictive factor to algal growth in Xin'anjiang Reservoir. In addition, the response of nutrients to Chla has spatial variabilities. Current results show the potential of Landsat 8 OLI data for estimating Chla in slight turbid reservoir and indicate that external pollution loading is an important driving force for the Chla spatiotemporal variability.

Understanding the changes and coupling characteristics between rural population (RP) and rural residential land (RRL) provides a theoretical basis for sustainable rural land use. Based on the index of human–land coupling development, this study analyzed the spatial–temporal characteristics and coupling types of RRL and RP on the levels of China's national and prefectural cities by using the data of official land use survey and demographic statistics from 2009 to 2016. Results showed that (a) China's RP is declining at an average annual rate of 2.07%, and the RP in most cities decrease from −3.33% to −1.20%. (b) The area of RRL in China constantly increased at an average annual rate of 0.56% and that of most cities has also maintained growth, with only 11.76% of cities that declined. (c) The per capita RRL in China increased from 267.96 m2 in 2009 to 325.58 m2 in 2016. The relationship between the RRL and RP in China was uncoordinated with a coupling type of G (rapid decline in RP and increase in RRL). The coupling types of most cities were also the uncoordinated type of G, and only less than 10% of cities had a coordinated type (Types B, C, D, and E). The results indicated that the coupling relationship between RP and RRL in China is decoupled and has obvious spatial heterogeneity, which could provide scientific support for optimizing land resources and coordinating human–land relationship in China's rural areas.

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