Spatial Variability of Microcystin Concentrations, 2009


Spatial patterns of large particulate (cell associated) and dissolved microcystins in Upper Klamath Lake directly reflect wind-driven current flow. Prevailing westerly to northwesterly winds create a dominantly clockwise circulation pattern in the lake that results in southward flow that is broad and shallow along the eastern shoreline and narrow flow northward through the deepest part of the lake (the trench) along the western shoreline (Wood and others, 2006, 2008). Previous work also has shown that the heaviest accumulation of phytoplankton (and the highest degree of cell senescence during periods of bloom decline) occurs in the deeper areas along the trench (Hoilman and others, 2008), which is the likely cause of high dissolved and particulate fraction microcystin concentrations measured at site MDT (table 3) in 2009. The highest concentrations of particulate nutrients and chlorophyll a also were measured at site MDT that year (chlorophyll a also was highest at site MDT in 2008; chlorophyll a data were not reported in 2007; Kannarr and others, 2010), which further indicates that the highest accumulation of buoyant colonies occurs along the western shoreline. Similar results have been reported in other studies of Upper Klamath Lake (Jassby and Kann, 2010; Kann, 2010). Northward flow through this area appears to have transported particulates to sites WMR and EPT, where relatively moderate to high concentrations of large particulate (cell associated) microcystins were measured. Likewise, shallow flow southward through the middle and eastern portion of the lake may have contributed to the occurrence of moderate dissolved and higher particulate microcystin concentrations at site RPT, the southernmost site (fig. 9). 


Between August 10 and September 14, 2009, samples for microcystin analysis were collected at discrete depths (one-quarter and three-quarters depths in the water column) at the deep sites, MDT and EPT, in order to determine whether microcystin concentrations varied in a consistent way with depth. However, the results of ANOVA and two-sample t-tests indicated no significant differences between microcystin concentrations (any size fraction) in samples from the upper and lower portions of the water column. In addition, no significant relation was found in correlation analyses between the microcystin concentrations (any size fraction) collected at the upper or lower depths and with nutrient (dissolved or particulate) concentrations collected at the same time and at the same depths (results not shown). 


First posted May 30, 2012