Effects of water depth and sediment nutrients on Vallisneria spinulosa in Lake Poyang

Abstract

Poyang Lake, the largest freshwater lake in China, has experienced a large decrease in wetland area due to long-term overutilization and especially after the hydrological drought events from 2003. This outdoor study was conducted to elucidate the impacts of drought and high concentrations of N on Vallisneria spinulosa. Compared with the 60 cm water depth, the 30 cm water depth caused no difference except lower leaf weight and greater winter bud number per plant growing in the sediment from Poyang Lake. After 400 mg/L NH4+-N was added to the sediment, the leaf weight, root weight, root length, winter bud number, ramet number and stolon weight of V. spinulosa declined greatly. The high NH4+-N content in sediment increased the influence of low water depth on V. spinulosa expressed as the relatively light fresh weight per winter bud of 0.11 g. The results indicated that both a low water depth in spring and high N concentration impacted V. spinulosa and the high concentration of NH4+-N limited the adaptation of V. spinulosa to the decline in water depths. Thus, besides water-level management, nutrient control is also required to protect and restore aquatic macrophytes in Poyang Lake.