Historical record of nutrients inputs into the Xin’an Reservoir and its potential environmental implication

Abstract

The Xin'an Reservoir is an important water supply source and water conservation area for the Qiantang River. However, after the occurrence of the two algae blooms in 1998 and 1999, the safety of water quality has been put into question. In order to study the historical deposition of nutrients, sediment cores were collected in different regions from the Xin'an Reservoir. The stable isotopes δC and δN, nutrients, total organic carbon (TOC), and inorganic carbon (IC) in the sediment cores were determined. Radiometric methods (Pb and Cs) were used to obtain sediment chronologies. Spatially, it was found that the average total nitrogen (TN) content in the upper 5 cm of sediments increased from 0.21% in the riverine zone, to 0.33%, and then to 0.57% in the lacustrine zone. The average TP content in the upper 5 cm increased from 0.67 g kg in the riverine zone, to 1.03 g kg in the estuary region, and then to 1.65 g kg in the lacustrine zone. In addition, TOC levels showed a distinct increase from 1.42% in the bottom to 5.97% in the surface of the lacustrine zone. These results demonstrated that although primary productivity and the input of nutrients constantly increased in recent years, algae blooms rarely occurred in the Xin'an Reservoir, due to "depth effect" and an aquatic environment protection-oriented fishery policy. However, high TOC flux and high bio-available phosphorus and nitrogen in surface sediment demonstrated that the reservoir is still confronted with the potential risk of algae blooms.

Factors that control the spatial and temporal distributions of phosphorus, nitrogen, and carbon in the sediments of a tropical reservoir

“…Greater turbulence in the fluvial and transition regions, together with shallower depths, would create an unstable depositional environment, as observed by Hou et al (2014) in Dalinouer Lake, China, and by Bartoszek and Tomaszek (2007) in Solina-Myczkowce Reservoirs, in Poland. In the dam area, however, the higher sedimentation rate (Cardoso- Silva et al 2016a) favors greater accumulation and retention of nutrients in the sediments (Jia et al 2017).…”

Spatiotemporal Dynamics of Nitrogen Transport in the Qiandao Lake Basin, a Large Hilly Monsoon Basin of Southeastern China

“…On the other hand, seasonal surface and lateral flows from non-point sources account for the majority of TN loads in the QLB, with crop, tea, and orchard lands together comprising nearly 40% of the total. The yield of TN from tea land exceeds that from other crop types, and although crop production is declining in the area [57,58], tea cultivation is rapidly expanding, both in the QLB and in other nearby basins with similar topography [27,31,59,60]. This is important because agricultural fertilizers are commonly applied in excessive amounts to tea and other intensively managed crops in the basin, especially the upper basin in Anhui Province [59][60][61][62][63].…”

“…The mean slope of the study area is 24.9°, and the area proportions of slopes < 10°, 10°-20°, 20°-25°, 25°-30°, and >30° are 22%, 13%, 9%, 12%, and 44%, respectively. Sediment loss from such highly erodible forested slopes in the QLB is known to be substantial [44], and the importance of these sediments in the release of TN is documented [57]. In contrast, orchards are currently a minor but growing land use category in the QLB.…”

An Integrative Framework to Control Nutrient Loss: Insights from Two Hilly Basins in China’s Yangtze River Delta

“…Three-quarters of the Qiandao Lake watershed remains forested, but grain production has declined significantly in recent decades [47], so that cropland now occupies just 8.3% of its area. Agriculture has nevertheless responded to rapid socio-economic development and correspondingly improved living standards by expanding in other ways.…”

“…Herein, we examine two hilly catchments in the YRD that are similarly threatened by humancaused N and P pollution, yet differ greatly in scale, intensity of management, and other contrasting characteristics [42][43][44][45][46][47]. This leads to practical insights for mitigation, not just in the YRD, but also in similar watersheds elsewhere [27].…”