Robert Jellison

Nutrient fluxes from upwelling and enhanced turbulence at the top of the pycnocline in Mono Lake, California

Time series measurements of temperature at 15 depths and profiles of temperature-gradient microstructure were obtained during a period with strong wind forcing and subsequent calm in Mono Lake, California. The wind forcing increased the amplitude of basin-scale internal waves and energy at all wave frequencies relative to the calm period. Rates of dissipation of turbulent kinetic energy, ∈, were high (∈ > 10−6 m2 s−3) at the top of the pycnocline at both an inshore and an offshore site on a day when winds reached 10 m s−1 and on the following two days at an inshore site (∈ > 10−7 m2 s−3). The enhanced turbulence occurred at the depth of a subsurface temperature maximum (zTM) and coincidentally with elevated concentrations of NH4, reduced concentrations of chlorophyll a and particulate carbon, and increased abundance of the macrozooplankter Artemia monica. The NH4 at zTM was more dispersed and of lower concentration inshore than offshore and indicated greater turbulent transport inshore. Over the course of 4 days, chlorophyll a concentrations increased in the upper mixed layer, and C:N and C:Chl ratios decreased. Offshore, the change in C:N ratio indicated a relaxation of moderate nutrient deficiency. We hypothesize that excretion by A. monica and turbulent transport of the NH4 from the subsurface temperature maximum led to improved physiological status of phytoplankton in the upper mixed layer.

Limnological conditions in Mono Lake: contrasting monomixis and meromixis in the 1990s

Mono Lake is a large, saline lake, located in the North American Great Basin and is subject to large variations in freshwater inflow as climatic conditions and diversion schemes have changed; consequently, major variations in chemical stratification occur. A transition from monomixis to meromixis occurred from 1994 to 1995. Lake-wide surveys of temperature, conductivity, dissolved oxygen, ammonium and chlorophyll profiles, Secchi depth and light attenuation, and Artemia monica abundances conducted throughout 1993, 1994, 1995, 1996 and 1997 document the contrasts between monomixis and meromixis. During the monomictic conditions in 1993 and 1994, the lake thermally stratified in March and mixed to the bottom by December, the hypolimnion became anoxic in late March and the water column was oxygenated to the bottom by December. During meromictic conditions in 1995, 1996 and 1997, the absence of holomixis during winter resulted in persistent anoxic conditions beneath the chemocline, an accumulation of ammonium in the monimolimnion and depletion in the mixolimnion, and low mixolimnetic chlorophyll concentrations in the spring and autumn. A comparison of the density differences between 2 and 28 m due to thermal versus chemical stratification indicated thermal stratification predominated in 1993 and 1994, while in 1995, 1996 and 1997 chemical stratification dominated the density differences. Ammonium, the limiting nutrient in Mono Lake, was lower in the upper mixed layer throughout 1996 and 1997 compared to the monomictic years, 1993 and 1994. During 1996 and 1997, the annual maxima in Secchi depths were among the deepest observed during the past 19 years, and reflected the lower phytoplankton abundance caused by decreased availability of nitrogen as a result of strong chemical stratification and the absence of a period of holomixis. In both 1996 and 1997, maturation of the spring generation of Artemia was slowed, peak abundance of the first generation of adult Artemia was a month later and percent ovigery, fecundity, and body size were reduced as compared to 1993 and 1994.

Photosynthetic activity of phytoplankton and its relation to environmental factors in hypersaline Mono Lake, California

The photosynthetic activity of phytoplankton in hypersaline Mono Lake, California was measured over the three year period, 1983–1985. The maximum chlorophyll-specific rate of carbon uptake (Pm B) and the lightlimited slope (alpha) were derived from laboratory measurements of photosynthesis vs. irradiance (P-1) relationships. Annual estimates of primary production were 340–540 g C m-2 yr-1. Production was two to three times higher during the spring of 1983 than in the springs of 1984 and 1985; higher standing biomass of algae occurred in 1983. While Pm B rates followed water temperatures and varied over 40-fold over the year, integral primary production varied less since periods of high Pm B occurred when algal biomass was low. Sixty-eight percent of the seasonal variation in the PmB was explained by a regression on temperature (53%), chlorophyll a (12%), and the carbon:chlorophyll a ratio (3%). Light-saturated and light-limited rates of photosynthesis generally covaried, evidenced by the strong seasonal correlation between Pm B and alpha. Sixty-one percent of variation in alpha was explained by a regression on Pm B, temperature, grazing, water column stability, and self-shading. There was no correlation of carbon uptake with ambient levels of inorganic nitrogen. The regression coefficient of the dependence of Pm B on the seasonal temperature trend was much larger than that determined from individual samples incubated at several different temperatures; this indicates that uptake is limited by more than low temperatures in the spring. Regression equations including only temperature, chlorophyll and depth were sufficient to estimate patterns of seasonal and year to year variation in integral primary productivity.

Nitrogen limitation and particulate elemental ratios of seston in hypersaline Mono Lake, California, U.S.A.

Particulate elemental ratios (C:N, N:P and C:Chl a) of seston in hypersaline (70–90 g kg−1) Mono Lake, California, were examined over an 11-year period (1990–2000) which included the onset and persistence of a 5-year period of persistent chemical stratification. Following the onset of meromixis in mid-1995, phytoplankton and dissolved inorganic nitrogen were substantially reduced with the absence of a winter period of holomixis. C:N, N:P and C:Chl a ratios ranged from 5 to 18 mol mol−1, 2 to 19 mol mol−1 and 25 to 150 g g−1, respectively, and had regular seasonal patterns. Deviations from those expected of nutrient-replete phytoplankton indicated strong nutrient limitation in the summer and roughly balanced growth during the winter prior to the onset of meromixis. Following the onset of meromixis, winter ratios were also indicative of modest nutrient limitation. A 3-year trend in C:N and N:P ratios toward more balanced growth beginning in 1998 suggest the impacts of meromixis weakened due to increased upward fluxes of ammonium associated with weakening stratification and entrainment of ammonium-rich monimolimnetic water. A series of nutrient enrichment experiments with natural assemblages of Mono Lake phytoplankton conducted during the onset of a previous episode of meromixis (1982–1986) confirm the nitrogen will limit phytoplankton before phosphorus or other micronutrients. Particulate ratios of a summer natural assemblage of phytoplankton collected under nitrogen-depleted conditions measured initially, following enrichment, and then after return to a nitrogen-depleted condition followed those expected based on Redfield ratios and laboratory studies.

Relationships between Artemia monica life history characteristics and salinity

Relationships between Artemia monica life history characteristics and salinity were determined using data from four published studies and three experiments presented here. Salinity explained 40 to 93 percent of the variation in ten life history characteristics. Reductions in hatching success, survival, length, weight, ovigery, and brood size were observed as salinity increased from 76 to 168 g l−1. Inter-brood duration, and time to hatching and reproduction were protracted as salinity was elevated. Salinity effects on life history characteristics appeared to be gradual and continuous rather than exhibiting thresholds. The one exception was naupliar survival, which was constant between 76 and 133 g l−1 followed by a decrease above 133 g l−1.

Re-appearance of rotifers in hypersaline Mono Lake, California, during a period of rising lake levels and decreasing salinity

The surface elevation of Mono Lake, California, rose ∼2 m and mixed-layer salinities declined about 5 g kg−1 during the 3 years (1995–1997) following the decision to restrict water diversions out of the Mono Basin. Abundant (18 000 m−2) Hexarthra jenkinae de Beauchamp were noted in pelagic samples in October 1997 after three decades of absence or very low abundance. Abundance subsequently increased to 100 000 m−2 in December 1997 before declining to low numbers through 1998 and 1999. The re-appearance of Branchionus plicatilis Muller in pelagic samples occurred in September 1998. B. plicatilis areal abundance increased to ∼15 000 m−2 in October–December of both 1998 and 1999 but was low throughout the rest of the year. Both rotifers were noted in nearshore ponds, but were only abundant in those with salinities below 53 g kg−1. During 1998–1999 when the salinities of the upper water column were 73–75 g kg−1, less saline shoreline habitats may have been seeding the offshore rotifer populations.

Artemia monica cyst production and recruitment in Mono Lake, California, USA

Annual egg production was determined for Artemia monica in Mono Lake, California, from 1983 to 1987. Annual oviparous (overwintering cyst) production was 3 and 7 million cysts m-2 yr-1 in 1986 and 1987, respectively, as measured by in situ sediment traps. Cyst production for the entire five year period was calculated using Artemia census data and inter-brood duration derived from mixolimnetic temperature. These estimates ranged from 2 to 5 million cysts m-2 yr-1. This method underestimated annual production by 30%, when compared to estimates using sediment traps. Cyst production was similar during 1983–1986 and showed a significant increase in 1987, which was due primarily to a larger reproductive population later in the year. Recruitment into the adult populations of the following spring ranged between 1.4 to 3.2%. Overall abundance of this generation reflected the patterns in annual cyst production. Compensatory effects must operate on the second generation of each year, since summer populations were similar in all years despite differences in cyst production.

Nearshore and pelagic abundances of Artemia monica in Mono Lake, California

The spatial distribution and abundance of the brine shrimp, Artemia monica, in Mono Lake, California were determined during 1982 and 1983. Peak abundances of shrimp occur in midsummer and reach densities of 15–17 individuals l-1 in the nearshore regions and 6–8 individuals 1-1 in the pelagic region. The brine shrimp were non-uniformly distributed both vertically and horizontally. The coefficient of variation in shrimp abundance among stations within the nearshore region was similar to that found in the pelagic region. On two of the nine dates, nearshore densities were 3 to 4 times greater than those in the pelagic zone, and on average the brine shrimp appear to be slightly over-dispersed to the nearshore region. However, including nearshore abundances in lakewide estimates will usually result in a change of less than a 10%.

Effect of benthic boundary layer transport on the productivity of Mono Lake, California

The significance of the transport of nutrient-rich hypolimnetic water via the benthic boundary layer (BBL) to the productivity of Mono Lake was studied using a coupled hydrodynamic and ecological model validated against field data. The coupled model enabled us to differentiate between the role of biotic components and hydrodynamic forcing on the internal recycling of nutrients necessary to sustain primary productivity. A 4-year period (1991–1994) was simulated in which recycled nutrients from zooplankton excretion and bacterially-mediated mineralization exceeded sediment fluxes as the dominant source for primary productivity. Model outputs indicated that BBL transport was responsible for a 53% increase in the flux of hypolimnetic ammonium to the photic zone during stratification with an increase in primary production of 6% and secondary production of 5%. Although the estimated impact of BBL transport on the productivity of Mono Lake was not large, significant nutrient fluxes were simulated during periods when BBL transport was most active.

IX international conference on Salt Lake research: Research opportunities and management challenges

The 9th International Conference on Salt Lake Research was held 26–30 September 2005 in Western Australia at the Curtin University of Technology, Perth, Australia. One hundred scientists from 10 countries presented research on a diverse array of topics highlighting research findings and opportunities, and management challenges associated with inland saline waters. Major emergent themes of the conference included modeling of ecosystem processes, microbial communities, and features of Western Australian inland saline environments, including current threats, conservation and management.