Total phosphorus thresholds for regime shifts are nearly equal in subtropical and temperate shallow lakes with moderate depths and areas

Abstract

SUMMARY1. Published research suggests that the total phosphorus (TP) thresholds for the regime shifts between a clear-water state dominated by submersed macrophytes and a turbid-water state dominated by phytoplankton in shallow lakes vary with forms of lake basins and climates. However, such hypotheses remain untested by direct field evidence. We therefore tested the hypotheses with empirical data from subtropical lakes on the Yangtze floodplain and also from other lakes in temperate to tropical zones. 2. TP thresholds were found to vary little at moderate depths, but to decrease notably when depth exceeds a level of probably 3-4 m, and increase sharply when depth is below a level of around 1-2 m. 3. TP thresholds were found to be nearly equal in shallow lakes 4. The threshold of turbidity for the forward shift was found to be higher than that for the backward shift, amending the previous hypothesis of the equality of turbidity thresholds for both shifts. 5. Our findings suggest that according to the subequality of TP thresholds, similar target concentrations for in-lake TP can be set in most shallow lakes world-wide to mitigate eutrophication.

Does the responses of Vallisneria natans (Lour.) Hara to high nitrogen loading differ between the summer high-growth season and the low-growth season?

“…) suggested to entail high risk of macrophyte loss in Yangtze shallow lakes (Wang et al, 2014) and the level (0.018 mg L −1 ) suggested as a threshold for a dominance shift from macrophytes to phytoplankton in Canadian lakes (Bayley et al, 2007). The relatively minor effect of nitrogen may be due to a weak development of periphyton compared with other studies showing a strong positive effect of nitrogen on periphyton growth (Özkan et al, 2010) and an associated decline in macrophyte growth (Olsen et al, 2015;Zhao et al, 2016).…”

“…Worldwide, with the increasing eutrophication of shallow lakes, a decline in the abundance of submersed macrophytes has often been seen (Körner, 2002;Ibelings et al, 2007;Wang et al, 2014), producing substantially negative impacts on the ecosystem structure, functioning, and services of shallow lakes (Scheffer, 1998;Jeppesen et al, 1998). Most scientists agree that phytoplankton shading promoted by increasing inputs of phosphorus is an underlying cause of the decreasing abundance, but the role of nitrogen has received increasing attention in recent years (Moss, 2001;Jeppesen et al, 2007;Moss et al, 2013).…”

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

“…However, the decline of submerged macrophytes continually happens in many eutrophic lakes throughout the world as a result of eutrophication with increasing nutrients [6,7]. It is well known that phosphorus (P) is often considered to be the most crucial growth limiting factor for plants in lakes [8,9], but the role of nitrogen (N) in submerged macrophytes recession has recently received increasing attention [10].…”

Macrophyte effects on algal turbidity in subtropical versus temperate lakes: a reply to Dolman (2014)

“…Dolman (2014) argued that our recent finding (Wang et al, 2014) of no marked effect of submerged macrophytes on the chlorophyll a (Chl a) to total phosphorus (TP) relationship in Yangtze subtropical lakes may not necessarily be valid due to the statistical procedure used to analyse the relationship between these two variables. 2.…”

“…argued that the apparent weak effect of macrophytes on relationship of phytoplankton chlorophyll a (Chl a) to total phosphorus (TP) in Yangtze subtropical lakes reported by Wang et al (2014) was actually due to a mistake in testing the difference in the heights of the lines (intercepts) at a point with low TP of 1 lg L À1 . Dolman (2014) further suggested that the features of fish communities suppressing macrophyteassociated zooplankton that cause a strong macrophyte effect in tropical lakes are absent in the Yangtze subtropical lakes.…”