Relationships between breeding waterbird abundance, diversity, and clear water status after the restoration of two shallow nutrient‐rich Danish lakes

Abstract

Breeding waterbird communities have suffered globally from the effects of anthropogenic changes in water quality (especially nutrient enrichment) in recent decades, but few studies have demonstrated the positive effects of restorative actions. Annual breeding waterbird surveys in the period 1977–2005 at two restored southern Danish lake basins (combining nutrient load reduction and biomanipulation) showed an up to five‐fold increase in abundance, and considerable changes in species richness and diversity, following restoration to clear water status in both lakes. Parallel surveys at a third lake, which retained clear water quality throughout, offering a form of natural ‘control', showed no such changes over the same time period. Consistent relationships between breeding waterbird abundance, species richness, and diversity with measures of water clarity (Secchi disc depth, chlorophyll a, and suspended matter) suggest that water clarity mainly drives the relationship; inverse relationships between these measures and total nitrogen and phosphorus were less consistent than for water clarity. The results suggest that an improvement in water clarity plays a key role in restoring breeding waterbird communities and suggest that breeding waterbirds can be indicators of the success of lake restoration projects, but more studies are needed to confirm their wider utility under a variety of conditions.

Differences in Waterbird Communities between Years Indicate the Positive Effects of Pen Culture Removal in Caizi Lake, a Typical Yangtze-Connected Lake

“…The results of previous studies showed that the water quality and zooplankton quickly recover after net pen removal, and conditions are more conducive to the growth of underwater vegetation [36,39,60]. Fox et al [26] reported that an increase in aquatic vegetation attracts a large number of waterbirds. Therefore, the increase in the waterbird abundance after purse seine removal in Caizi Lake may be attributed to the substantial recovery of aquatic vegetation [46].…”

“…Habitat restoration measures are expected to benefit waterbirds, from individuals to populations, and at the community level. The results of multiple studies showed that wetland restoration can increase the carrying capacity of waterbirds and the species diversity of assemblages [25][26][27]. However, some researchers have reported the failure or low efficiency of restoration measures [28].…”

Borrowing from the palaeolimnologists toolkit; the use of lake sediment cores in diagnosing the causes of freshwater species decline

“…A significant land use change in the Flow Country during the 1970s and 1980s was the introduction of commercial forestry, which led to thousands of hectares of peatland being planted with non-native tree species, primarily Sitka spruce (Picea sitchensis) and Lodgepole pine (Pinus contorta) (Stroud et al, 1988). There are two primary mechanisms via which afforestation of the lake catchments could negatively influence breeding common scoter; either by changing water chemistry (particularly water clarity) which has been shown to be correlated with abundance of breeding waterbirds in other studies (Fox et al, 2020) or by providing habitat for predators directly feeding on the birds themselves (Holopainen et al, 2021;Holopainen et al (submitted) 1 ).…”

Feedback between climate change and eutrophication: revisiting the allied attack concept and how to strike back

“…One such method is biomanipulation, including removal of planktivorous and benthivorous fish. In northern temperate lakes in Europe biomanipulation has had variable long-term effectiveness (Jeppesen et al 2012), but a shift to clear water and promotion of non-cyanobacterial species, along with submerged plants and higher biodiversity, is frequent (Fox et al 2020). Biomanipulation in subtropical and tropical lakes is often less successful mainly due to trophic web structure (reviewed in Jeppesen et al, 2012), which may indicate that its future success under warmer conditions may be weaker or shorter-lived than needed.…”