Seasonal Dynamics of Nutrient Loading and Chlorophyll A in a Northern Prairies Reservoir, Saskatchewan, Canada

Abstract

Harmful algae blooms have become an increasing concern in context to the safety of water resources around the globe; however, little is known about the dynamics and specific causes of such blooms in the prairie ecozone in North America. The aim of this study was to research the nitrogen (N) and phosphorous (P) content and nutrient limitation (defined as N and P limitation) of growth of cyanobacteria in a northern prairies reservoir (Lake Diefenbaker [LD], SK, Canada). A combination of concentration balance analysis for N and P, controlled bioassays with the natural consortium of phytoplankton or defined monocultures of cyanobacteria, and satellite imagery was applied to address this aim. The current trophic status of Lake Diefenbaker is one of moderate eutrophication. Primary production in the lake is P-limited, and N did not represent a limiting factor for algal production. There was no significant increase in TP concentrations between the upper and lower portions of the reservoir, indicating that most of the phosphorus in LD comes from upstream sites in Alberta. Anabaena circinalis, a species that has the potential to seriously degrade lake ecosystems, was identified as the predominant cyanobacteria in LD. Together with the fact that total P (TP) influxes into the reservoir primarily originate from upstream sources, these results suggest the need for remedial measures in the upstream reach of the South Saskatchewan River. Satellite imaging represented a promising approach in support of monitoring for potential algal blooms in LD; however, due to limited sensitivity and issues associated with atmosphere interference this methodology should only be used in combination with in situ water quality monitoring. In summary, while this study indicated that Lake Diefenbaker is potentially at risk from blooms with cyanobacteria (some of which such as Anabena sp. that can produce toxins) during late summer and fall, development of clear causal relationships and risk assessment strategies is currently limited due to lack of monitoring data and programs.

Change in nutrient loading pattern due to coupled effect of change in concentration and hydroclimatic forces

“…It has been shown that occurrence of drought conditions (low inflow and flushing rate) after high nutrient loads from high flow events can promote cyanobacterial blooms in lakes and reservoirs (Paerl and Huisman 2009). This is supported by observed cyanobacterial blooms in LD during years with low flow conditions (SEPS & EC 1988;Hecker et al 2012;Hudson and Vandergucht 2015).…”

Decadal regulation of phytoplankton abundance and water clarity in a large continental reservoir by climatic, hydrologic and trophic processes

“…on the South Saskatchewan River, Canada, and which serves as headwater to Qu'Appelle River drainage basin (Hall et al, 1999a;Hecker et al, 2012). The reservoir's catchment which lies mainly within Alberta, Saskatchewan, and upstate Montana was originally mixed-grass Prairie, but it is presently under predominantly (~65%) agricultural land use (cereal crops, pasture, livestock) (Hall et al, 1999a).…”

“…In general, the embayment warms slowly and is polymictic although in some years limited thermal stratification is observed during late-July or August (Dröscher et al, 2009;Hudson and Vandergucht, in this issue). Phytoplankton are characteristic of well-mixed mesotrophic lakes with abundant diatoms in spring giving way to later-summer assemblages of flagellates and occasional cyanobacteria (Hecker et al, 2012;McGowan et al, 2005b;Patoine et al, 2006). The zooplankton community is composed mainly of cyclopoid (Diacyclops thomasii) and calanoid (Leptodiaptomus siciloides) copepods, but also includes large (Daphnia pulex, Daphnia galeata mendotae, Diaphanosoma birgei, Holopedium gibberum) and small (Bosmina longirostrus, Daphnia retrocurva) cladocerans at lower densities .…”

“…During this latter transition, water-column chlorophyll (Chl a) increased from~1 μg/L in 1984 to~5 μg/L in 1994 (Environment Canada, 1988). Recent publications suggest that modern phytoplankton abundance has remained elevated (McGowan et al, 2005b;Patoine et al, 2006) and that colonial cyanobacteria may be problematic (Hecker et al, 2012), although there has been no comprehensive evaluation of water quality change since the mid-1990s. Whole-basin carbon budgets demonstrate that Lake Diefenbaker has been net heterotrophic (respiration N primary production) during the past 20 years (but see Quiñones-Rivera et al, in this issue), although CO 2 sequestration has increased since ca.…”

Socio-hydrology and the science–policy interface: a case study of the Saskatchewan River basin

“…Data from 18 monitoring stations between 1973 and 2007 show especially high phosphorous levels downstream from Alberta's intensive agricultural areas and feedlots but much lower levels downstream from Lake Diefenbaker in Saskatchewan. Data from the period 2011-2012 indicate that 90 % of the incoming phosphorous is retained in Lake Diefenbaker where eutrophication is of increasing concern (Hecker et al, 2012). The Saskatchewan River ultimately discharges to Lake Winnipeg, which receives a major load of nutrients from the USCanadian trans-boundary Red River.…”