Interdecadal declines in flood frequency increase primary production in lakes of a northern river delta

Abstract

Human activities and climate change have greatly altered flooding regimes in many of the world's river deltas, but the impact of such changes remains poorly quantified on decadal to multidecadal timescales. This study identified the response of delta lake primary production (measured as the concentration of sedimentary pigments) to variations in flood frequency using spatial surveys and paleolimnological analyses of lakes in the Peace-Athabasca Delta (PAD), Canada. Surveys of 61 lakes spanning a range of hydrological conditions showed that those lakes that received flood waters less frequently were associated with elevated algal production (surface sedimentary pigments) and, in some lakes, increased growth of emergent macrophytes and epiphytic diatoms. Paleolimnological analyses of five lakes corroborated the contemporary spatial survey results by showing that production of pigments from most algal groups increased during recent periods of lower flood frequency in the 20th century as determined from increases in cellulose-inferred lake-water oxygen isotope composition and plant macrofossils, but remained stable in a 'reference' basin. In general, past periods of elevated algal production coincided with the increased abundance of submerged macrophytes or emergent vegetation that provide habitat for attached algae. These results suggest that interdecadal declines in river discharge arising from increased aridity, hydrologic regulation or consumptive water use will cause long-term increases in primary production and alter ecosystem processes (carbon sequestration, biological diversity) in aquatic delta ecosystems similar to the PAD where lakes become nutrient-rich in the absence of flooding.

Timescales of hydrolimnological change in floodplain lakes of the Peace‐Athabasca Delta, northern Alberta, Canada

“…Pulse flood events raise lake water concentrations of suspended sediments, TP, SO 4 and DSi and reduce water clarity and concentrations of dissolved nutrients, DOC and ions. On the basis of our study, this transition to increasing hydrologic closure of PAD lakes will be accompanied by an increase in water transparency and bio-available forms of nutrients which will promote primary production, a finding consistent with that of McGowan et al (2011). At this short timescale, concentrations of DOC, SO 4 , TKN and ions do not change appreciably.…”

“…This transition has begun in the more elevated portions of the Athabasca sector, such as observed at PAD 23, and is likely to become more widespread (Wolfe et al, 2008a). On the basis of our study, this transition to increasing hydrologic closure of PAD lakes will be accompanied by an increase in water transparency and bio-available forms of nutrients which will promote primary production, a finding consistent with that of McGowan et al (2011).…”

“…with periodic river connectivity) have intermediate concentrations (Wolfe et al, 2007b). Consistent with this pattern, analysis of photosynthetic pigment concentrations in the surface sediments found that closed-drainage lakes have higher algal production than lakes that flood more frequently (McGowan et al, 2011). Wolfe et al's (2007b) one-time regional survey was conducted at the end of the ice-free season, which likely under-represents the influence of important hydrological processes that occur during the spring freshet (i.e.…”

“…On the basis of a regional survey of water chemistry and water isotope composition in 61 lakes conducted in October 2000, closed-drainage lakes (i.e. Consistent with this pattern, analysis of photosynthetic pigment concentrations in the surface sediments found that closed-drainage lakes have higher algal production than lakes that flood more frequently (McGowan et al, 2011). with continuous river connection), whereas restricted-drainage lakes (i.e.…”

Fluctuated water depth with high nutrient concentrations promote the invasiveness ofWedelia trilobatain Wetland

“…Waterlogging or change in the water depth resulting from hydrological turbulences is a common stress for plants in wetland ecosystems (McGOWAN et al, 2011;Yuan, Yang, Liu, & Wang, 2017). The climate change is a strong reason for the hydrological disturbances such as tidal variation, flooding, and severe drought.…”