Effects of mooring management on submerged vegetation, sediments and macro-invertebrates in Lake Constance, Germany

Abstract

Mooring areas are a common form of berthing in many of Germany's inland waters for the growing number of sporting boats. A circular swinging zone around the anchor zone is formed, in which the submerged macrophyte vegetation is destroyed to a large extent, and the sediment surface is eroded. We investigated the effects of two types of buoy (conventional and so-called hook-buoys) in comparison with undisturbed reference sites nearby. The aim of the study was to identify possible harmful consequences of mooring sites to lake littoral habitats in Lake Constance-Untersee, and to provide information to managers to aid them in the formulation of mooring management plans with the least ecological impact. The study focused on submerged vegetation, surface sediments and macro-invertebrate colonisation. In the swinging circle of conventional buoys (87 m 2 ) we observed a significant sediment matter erosion of 0.9 tonnes and a reduction of organic matter amount by 4.5% of the undisturbed reference. The vegetation free area increased by 122%, and the phytomass (mainly Chara div. spp.) was reduced by 14.6% per berth. The psammophilous macro-invertebrate numbers were not significantly affected (-3%) in contrast to the phytophilous taxa which were reduced by 12.7% per berth. The mayfly larvae were the most negatively affected taxon. Oligochaetes profited from the clearing of the sediment surface in the swinging circles. The ecological effects of the hook-buoys were more minor, mainly due to the smaller swinging circle (6 m 2 ). We concluded that the detrimental effects of mooring can be significantly reduced by mooring systems, e. g. the hookbuoy system as it was used in this study, which reduce the area disturbed and cleared by the anchor chain. We argue that these results can be generalised to mooring areas with soft bottom and dense macrophyte vegetation in Lake Constance and other large lakes.

Effects of boat traffic and mooring infrastructure on aquatic vegetation: A systematic review and meta-analysis

“…Six of the articles reporting effects from mooring buoys were performed in coastal seagrass meadows (Montefalcone et al 2006;Demers et al 2013;La Manna et al 2015;Colomer et al 2017;Unsworth et al 2017;Glasby and West 2018) and the remaining one in a charophyte-dominated vegetation community in a lake (Ostendorp et al 2009). Five different mooring types were studied.…”

“…For swing moorings, the size of the scar depended on the length of the bottom chain (e.g. Ostendorp et al 2009;Glasby and West 2018). Consequently, the ''hook buoy'' that allowed adjustment of the chain length to the water level, strongly decreased the scar size (from an average of 87 to 6 m 2 ) in a freshwater system with fluctuating water level (Ostendorp et al 2009).…”

“…Ostendorp et al 2009;Glasby and West 2018). Consequently, the ''hook buoy'' that allowed adjustment of the chain length to the water level, strongly decreased the scar size (from an average of 87 to 6 m 2 ) in a freshwater system with fluctuating water level (Ostendorp et al 2009). The most extensive scars were created by the ''cyclone mooring'' with three long chains (Demers et al 2013).…”

“…This means that the damage from a single buoy can be reduced by decreasing the bottom area that is exposed to moving chains. For instance, Ostendorp et al (2009) showed that conventional swing moorings caused loss of vegetation cover over a 15 times larger bottom area than buoys with adjustable chain length. The only mooring type in our data that was designed to move without a dragging chain (''screw mooring'' with a moving rod elevated from seabed; Fig.…”

“…Anchoring and mooring buoys create mechanical damage to the vegetation and stir up sediment (e.g. Hastings et al 1995;Ostendorp et al 2009;Unsworth et al 2017). Dock constructions result in shading of the bottom under the dock (Campbell and Baird 2009;Eriander et al 2017) and can change hydrodynamic conditions, resulting in erosion and translocation of sediment (Dugan et al 2011).…”