Response of Vallisneria natans to Increasing Nitrogen Loading Depends on Sediment Nutrient Characteristics

Abstract

High nitrogen (N) loading may contribute to recession of submerged macrophytes in shallow lakes; yet, its influences vary depending on environmental conditions. In August 2013, we conducted a 28-day factorial-designed field mesocosm experiment in Lake Taihu at the Taihu Laboratory for Lake Ecosystem Research (TLLER) to examine the effects of high N loading on the growth of Vallisneria natans in systems with contrasting sediment types. We ran the experiments with two levels of nutrient loading-present-day external nutrient loading (average P: 5 µg·L −1 ·day −1 , N: 130 µg·L −1 ·day −1 ) and P: 5 µg·L −1 ·day −1 , and with three times higher N loading (N: 390 µg·L −1 ·day −1 ) and used sediment with two contrasting nutrient levels. V. natans growth decreased significantly with increasing N loading, the effect being dependent, however, on the nutrient status of the sediment. In low nutrient sediment, relative growth rates, leaf biomass and root biomass decreased by 11.9%, 18.2% and 23.3%, respectively, at high rather than low N loading, while the decline was larger (44.0%, 32.7% and 41.8%, respectively) when using high nutrient sediment. The larger effect in the nutrient-rich sediment may reflect an observed higher shading of phytoplankton and excess nutrient accumulation in plant tissue, though potential toxic effects of the high-nutrient sediment may also have contributed. Our study confirms the occurrence of a negative effect of increasing N loading on submerged plant growth in shallow nutrient-enriched lakes and further shows that this effect is augmented when the plants grow in nutrient-rich sediment. External N control may, therefore, help to protect or restore submerged macrophytes, especially when the sediment is enriched with nutrients and organic matter.

Lake Restoration and Management in a Climate Change Perspective: An Introduction

“…[11,27]); yet, its influences vary depending on environmental conditions. In a study presented in this special issue [28], an investigation was undertaken of whether the effect of high N loading on Vallisneria natans growth in systems depended on the nutrient status of the sediment in subtropical lakes. Growth of V. natans was observed to decrease significantly with increasing N loading.…”

“…In warm lakes, however, enhanced top-down control by zooplankton is not to be expected as high recruitment of fish and dominance of small fish will prevent large-bodied zooplankton from becoming dominant [7,28,30]. Recently, transplantation of submerged macrophytes as a supplementary measure to fish removal has been applied to restore warm Chinese shallow lakes in order to compensate for the expected lack of increasing grazing control of phytoplankton after biomanipulation in warm lakes.…”

“…Recently, transplantation of submerged macrophytes as a supplementary measure to fish removal has been applied to restore warm Chinese shallow lakes in order to compensate for the expected lack of increasing grazing control of phytoplankton after biomanipulation in warm lakes. These two measures combined have successfully shifted warm lakes to a clear water state [28], but little is known about the responses to restoration of key physico-chemical variables. An analysis was made of the seasonal variation in nutrient concentrations in two subtropical and one tropical biomanipulated shallow Chinese lake subjected to restoration [31].…”

Interactive Effects of Rising Temperature and Nutrient Enrichment on Aquatic Plant Growth, Stoichiometry, and Palatability

“…Both warming (temperature rise) and eutrophication (nutrient enrichment) affect aquatic plant nutrient content and subsequent stoichiometry. Nutrient enrichment in the environment significantly increases the plant nutrient content (Dorenbosch and Bakker, 2011;Dülger et al, 2017), and decreases the C:nutrient ratios (Gu et al, 2016;Velthuis et al, 2017;Gu et al, 2018). However, studies on the impact of warming on aquatic plant C:nutrient ratios are scarce and yield contradictory results (Cross et al, 2015;Velthuis et al, 2017).…”

The Biomass and Physiological Responses of Vallisneria natans (Lour.) Hara to Epiphytic Algae and Different Nitrate-N Concentrations in the Water Column

“…Ammonia-N is the dominant N form in the interstitial water, while nitrate-N usually exists in much higher concentrations in the overlying water [17]. Rooted submerged macrophytes are capable of taking up NH 4 + and NO 3 − through both roots and shoots from ambient environments [18,19]. Burkholder et al [20] found that water-column nitrate enrichment promoted the decline of eelgrass Zostera marina.…”