Response of Submerged Macrophyte Communities to External and Internal Restoration Measures in North Temperate Shallow Lakes

Abstract

Submerged macrophytes play a key role in north temperate shallow lakes by stabilizing clear-water conditions. Eutrophication has resulted in macrophyte loss and shifts to turbid conditions in many lakes. Considerable efforts have been devoted to shallow lake restoration in many countries, but long-term success depends on a stable recovery of submerged macrophytes. However, recovery patterns vary widely and remain to be fully understood. We hypothesize that reduced external nutrient loading leads to an intermediate recovery state with clear spring and turbid summer conditions similar to the pattern described for eutrophication. In contrast, lake internal restoration measures can result in transient clear-water conditions both in spring and summer and reversals to turbid conditions. Furthermore, we hypothesize that these contrasting restoration measures result in different macrophyte species composition, with added implications for seasonal dynamics due to differences in plant traits. To test these hypotheses, we analyzed data on water quality and submerged macrophytes from 49 north temperate shallow lakes that were in a turbid state and subjected to restoration measures. To study the dynamics of macrophytes during nutrient load reduction, we adapted the ecosystem model PCLake. Our survey and model simulations revealed the existence of an intermediate recovery state upon reduced external nutrient loading, characterized by spring clear-water phases and turbid summers, whereas internal lake restoration measures often resulted in clear-water conditions in spring and summer with returns to turbid conditions after some years. External and internal lake restoration measures resulted in different macrophyte communities. The intermediate recovery state following reduced nutrient loading is characterized by a few macrophyte species (mainly pondweeds) that can resist wave action allowing survival in shallow areas, germinate early in spring, have energy-rich vegetative propagules facilitating rapid initial growth and that can complete their life cycle by early summer. Later in the growing season these plants are, according to our simulations, outcompeted by periphyton, leading to late-summer phytoplankton blooms. Internal lake restoration measures often coincide with a rapid but transient colonization by hornworts, waterweeds or charophytes. Stable clear-water conditions and a diverse macrophyte flora only occurred decades after external nutrient load reduction or when measures were combined.

Exploring environmental predictors of aquatic macrophytes in water‐dependent Natura 2000 sites of high conservation value: Results from a long‐term study of macrophytes in Greek lakes

“…show that phosphorus had a strong effect on PVI%, indicating that (Bakker, Sarneel, Gulati, Liu, & van Donk, 2013;Hilt et al, 2018). The present study also shows the high abundance of…”

“…These results also show that phosphorus had a strong effect on PVI%, indicating that the trophic state is related to abundant assemblages that occupy a large fraction of the water column. This is commonly observed in shallow eutrophic lakes where, under clear‐water conditions, fast‐growing eutrophic species such as Ceratophyllum demersum may become dominant, leading to an extensive cover of macrophytes, but with low diversity (Bakker, Sarneel, Gulati, Liu, & van Donk, ; Hilt et al, ). The present study also shows the high abundance of Ceratophyllum demersum, confirming the trend of this species to dominate macrophyte assemblages.…”

Phosphorus Availability and Growth of Benthic Primary Producers in Littoral Lake Sediments: Are Differences Linked to Induced Bank Filtration?

“…In parallel with the high nutrient loading, almost all macrophytes disappeared from Lake Müggelsee in the 1970s. After the nutrient reduction started, however, no significant recovery of macrophyte abundance and species diversity was seen for about 20 years despite increasing water transparency, especially during spring [22]. Light attenuation by high periphyton biomass was significantly contributing to this delay [23].…”

“…The macrophyte population was dominated by Stuckenia pectinata (formerly known as Potamogeton pectinatus), a species known for survival under turbid conditions in shallow littoral areas of highly eutrophic lakes [22]. Only after around 2006, macrophyte maximum colonization depth and biomass started increasing [22] due to decreasing periphyton biomass (unpublished data). Periphyton biomass, however, is still high (unpublished data).…”

Status of aquatic and riparian biodiversity in artificial lake ecosystems with and without management for recreational fisheries: implications for conservation

“…For example, the diversity of submerged macrophytes is strongly governed by nutrient inputs (which 18 is fundamentally related to land use and hydrology at catchment scales) and in-water chemical 19 variables, sediments and water turbidity (which affects light penetration) (Hilt et al, 2018;Stefanidis, 20 Sarika, & Papastegiadou, 2019). However, submerged macrophytes can also be negatively affected 21 by benthivorous fish (Bajer et al, 2016) and herbivory, e.g.…”