Annual winter water‐level drawdowns influence physical habitat structure and macrophytes in Massachusetts, USA, lakes

Abstract

Annual wintertime water‐level drawdowns are a common management strategy in recreational lakes; however, few studies have estimated their relative impact on lake littoral habitat among a set of typically co‐occurring anthropogenic stressors including lakeshore development and herbicide application. Within 21 Massachusetts, USA lakes that represented a drawdown magnitude gradient (0.07–2.26 m), we assessed depth‐specific littoral habitat (coarse wood, sediment, macrophytes) at two sites adjacent to forested or developed shorelines. Using generalized linear mixed models, we found coarse wood abundance and branching complexity was not correlated with drawdown magnitude but was primarily explained by the presence of lakeshore development. Drawdown magnitude was negatively correlated with silt cover and positively correlated with coarse substrate cover, with effects further varying by depth (0.5 m vs. 1 m). Macrophyte biomass and biovolume were negatively correlated with drawdown magnitude with effects also varying by depth for biomass. Macrophyte taxa with annual longevity strategies (e.g., Najas flexilis) and amphibious growth forms increased in biomass proportions with drawdown magnitude. Distance‐based redundancy analyses suggested macrophyte taxa composition was driven by drawdown magnitude, coarse substrate, alkalinity, water transparency, and herbicide use. These results suggest the importance of water quality and depth on macrophyte assemblage responses to winter drawdowns and the potential to develop drawdown‐tolerant macrophyte assemblages. Altogether, understanding the unique impacts of anthropogenic stressors on littoral zone habitat across heterogeneous environmental lake conditions can help minimize impacts to lake ecological integrity while maintaining recreational value.

A Multi-Sensor Approach to Characterize Winter Water-Level Drawdown Patterns in Lakes

“…The data and analysis framework developed for MA can serve as a template for assessing drawdown practices in other parts of the world, which is not feasible with in situ monitoring alone. The ability to detect WD carries many potential management applications, such as evaluating effects on near-shore habitats and relationships to lake water quality [2,35]. The information on drawdown frequency and metrics can aid water managers and policy makers in setting guidelines for balancing the intended benefits of drawdowns for nuisance plant control and infrastructure protection versus the potential ecological impacts of these artificial water-level manipulations [9].…”

“…Most WD lakes implement drawdowns in the fall by releasing water downstream when river flows are lowest. Past research indicates that the timing of these drawdowns, which coincide with the region's seasonal precipitation and temperature patterns, can significantly impact physical habitat structure and macrophytes in Massachusetts lakes [35]. The overall methods including data collection, processing, and analysis steps involved to achieve the objectives of this study are shown in Figure 2.…”

“…These results concur with the findings of Carmignani et al [2] who concluded that drawdowns are primarily based on management decisions rather than climate factors. Although our study did not survey lake managers, documented reasons for conducting drawdowns include aquatic plant control, fisheries management, infrastructure maintenance, and waterfront access [35]. Additional social surveys across private and public lake managers could provide further insights into motivations behind drawdown decisions each year.…”

“…Some drawdown studies have calculated similar water-level metrics using in situ data [1,2], but the remote sensing-derived measurements allow assessment at broader scales. Quantifying drawdown timing, magnitude, duration, and lake exposure area provides tangible metrics for evaluating ecological impacts and comparing across years and lakes [35].…”

Effect of Gated Weir Opening on the Topography and Zooplankton Community of Geum River, South Korea

“…In order to clearly identify the community composition and spatiotemporal distribution of cladocerans and copepods in a river, it is important to investigate the relationship between these communities and the structure of their microhabitat. As the physical microhabitat structure of freshwater ecosystems mainly depends on aquatic macrophytes [31,32], the abundance of these organisms must also be considered.…”