A functional definition to distinguish ponds from lakes and wetlands

Abstract

Ponds are often identified by their small size and shallow depths, but the lack of a universal evidence-based definition hampers science and weakens legal protection. Here, we compile existing pond definitions, compare ecosystem metrics (e.g., metabolism, nutrient concentrations, and gas fluxes) among ponds, wetlands, and lakes, and propose an evidence-based pond definition. Compiled definitions often mentioned surface area and depth, but were largely qualitative and variable. Government legislation rarely defined ponds, despite commonly using the term. Ponds, as defined in published studies, varied in origin and hydroperiod and were often distinct from lakes and wetlands in water chemistry. We also compared how ecosystem metrics related to three variables often seen in waterbody definitions: waterbody size, maximum depth, and emergent vegetation cover. Most ecosystem metrics (e.g., water chemistry, gas fluxes, and metabolism) exhibited nonlinear relationships with these variables, with average threshold changes at 3.7 ± 1.8 ha (median: 1.5 ha) in surface area, 5.8 ± 2.5 m (median: 5.2 m) in depth, and 13.4 ± 6.3% (median: 8.2%) emergent vegetation cover. We use this evidence and prior definitions to define ponds as waterbodies that are small (< 5 ha), shallow (< 5 m), with < 30% emergent vegetation and we highlight areas for further study near these boundaries. This definition will inform the science, policy, and management of globally abundant and ecologically significant pond ecosystems.

Classifying Mixing Regimes in Ponds and Shallow Lakes

“…We identified that small, shallow waterbodies have a variety of mixing regimes, and can no longer be assumed to be continuously polymictic. Rather, we propose a new paradigm where temperate shallow waterbodies have three mixing regimes (Figure 9), which are likely functionally distinct in ecological and biogeochemical processes (Fairchild et al, 2005;Richardson et al, 2022). First, larger shallow lakes that continuously mix are distinguished from smaller ponds that commonly stratify.…”

“…As a result, the boundary between whether a waterbody is mixed or stratified increases as a function of increasing area and depth (Gorham & Boyce, 1989; Kirillin & Shatwell, 2016; Lathrop & Lillie, 1980). While smaller waterbodies on the scale of a few hectares or less (commonly referred to as “ponds”; Richardson et al., 2022) have been excluded from these predictive frameworks, surface area and depth may similarly regulate mixing. For instance, large and shallow lakes may mix frequently, whereas ponds may often stratify due to sheltering from the surrounding topography and vegetation (Andersen et al., 2017; Chimney et al., 2006; Markfort et al., 2010).…”

Influence of macrophytes on stratification and dissolved oxygen dynamics in ponds

“…The ponds are rectangular, relatively small (surface area 400 m 2 at the water line; Figure 1), and shallow (maximum depth 2 m and mean depth 0.8 m), with simple, bowl-shaped bathymetries. These waterbodies fit morphometric and functional definitions of ponds (Richardson et al 2022). Water balance is driven solely from precipitation and evaporation as there are no surface inflows or outflows and the ponds are lined with bentonite to prevent groundwater interactions.…”

Heterogenous controls on lake color and trends across the high-elevation U.S. Rocky Mountain region

“…For example, some green/brown lakes occurred in cold areas (MAAT<4.5ºC) if they were shallow (<2.5m average depth), particularly if they had larger watersheds (>12.5km 2 ). This is expected since small, shallow lakes tend to be more productive than deep lakes (Duarte and Kalff, 1989;Genkai-Kato and Carpenter, 2005;Richardson et al, 2022). Conversely, in some shallow lakes, the color that satellites detect may be capturing benthic algal growth, which can make up a majority of the lake productivity in systems where photic zone extends to the benthos (Lõugas et al, 2020).…”