Heterotrophic N2-fixation contributes to nitrogen economy of a common wetland sedge, Schoenoplectus californicus

A survey of the ecological variability within 52 populations of Schoenoplectus californicus (C.A. Mey.) Soják across its distributional range revealed that it is commonly found in nitrogen (N) limited areas, but rarely in phosphorus limited soils. We explored the hypothesis that S. californicus supplements its nitrogen demand by bacterial N2-fixation processes associated with its roots and rhizomes. We estimated N2-fixation of diazotrophs associated with plant rhizomes and roots from several locations throughout the species’ range and conducted an experiment growing plants in zero, low, and high N additions. Nitrogenase activity in rhizomes and roots was measured using the acetylene reduction assay. The presence of diazotrophs was verified by the detection of the nifH gene. Nitrogenase activity was restricted to rhizomes and roots and it was two orders of magnitude higher in the latter plant organs (81 and 2032 nmol C2H4 g DW-1 d-1, respectively). Correspondingly, 40x more nifH gene copies were found on roots compared to rhizomes. The proportion of the nifH gene copies in total bacterial DNA was positively correlated with the nitrogenase activity. In the experiment, the contribution of fixed N to the plant N content ranged from 13.8% to 32.5% among clones from different locations. These are relatively high values for a non-cultivated plant and justify future research on the link between N-fixing bacteria and S. californicus production

Harmful Algal Blooms Threaten the Health of Peri-Urban Fisher Communities: A Case Study in Kisumu Bay, Lake Victoria, Kenya

Available guidance to mitigate health risks from exposure to freshwater harmful algal blooms (HABs) is largely derived from temperate ecosystems. Yet in tropical ecosystems, HABs can occur year-round, and resource-dependent populations face multiple routes of exposure to toxic components. Along Winam Gulf, Lake Victoria, Kenya, fisher communities rely on lake water contaminated with microcystins (MCs) from HABs. In these peri-urban communities near Kisumu, we tested hypotheses that MCs exceed exposure guidelines across seasons, and persistent HABs present a chronic risk to fisher communities through ingestion with minimal water treatment and frequent, direct contact. We tested source waters at eleven communities across dry and rainy seasons from September 2015 through May 2016. We measured MCs, other metabolites, physicochemical parameters, chlorophyll-a, phytoplankton abundance and diversity, and fecal indicators. We then selected four communities for interviews about water sources, usage, and treatment. Greater than 30% of source water samples exceeded WHO drinking water guidelines for MCs (1 µg/L), and over 60% of source water samples exceeded USEPA guidelines for children and immunocompromised individuals. 50% of households reported a sole source of raw lake water for drinking and household use, with alternate sources including rain and boreholes. Household chlorination was the most widespread treatment utilized. At this tropical, eutrophic lake, HABs pose a year-round health risk for fisher communities in resource -limited settings. Community-based solutions and site-specific guidance for Kisumu Bay and similarly impacted regions is needed to address a chronic health exposure likely to increase in severity and duration with global climate change

Potential of Long-lead Streamflow and Drought Forecasting in California

We investigated the roles of three tall emergent macrophytes (Scirpus acutus, S. californicus and Typha domingensisi in carbon cycling at a local wetland constructed for wastewater treatment and at an adjacent stream fed freshwater marsh. Combined above ground standing biomass ranged from 1125 g/m2 in freshwater to 3192 g/m2 in wastewater. Scirpus acutus (SA) densities ranged from 86 plants/m- in freshwater to 206 plants/m2 in wastewater. A combination of T. doming ens is and T. latifolia (TS) densities ranged from zero plants/m2 in wastewater and freshwater to 19 plants/m2 in wastewater. Growth rates of SA were highest for plants between 50 to 100 em and the average maximum rate was 6 cm/day. For TS the highest rates were recorded for plants between 0 and 50 ern and the average maximum rate was 4.5 ern/day. Growth for both SA and TS slows at heights between 2.5 and 3 m. Both SA and TS are subjected to grazing, TS more so than SA and there is no difference if they are in freshwater or wastewater. Carbon to nitrogen ratios vary throughout the year with the fall ratios indicating much higher carbon in the above ground biomass. Decomposition rates of above ground material in the water column vary within the wastewater treatment system with material closer to the inflow of wastewater having slower rates than those furthest from the inflow. Decomposition of below ground biomass, buried at -15 cm, is much faster for TS than for SA.A mesocosm study investigating biomass and nutrient allocations indicates that the ratio of above ground biomass to below ground biomass changes with nutrient availability. In low nutrient situations the ratio for SA and T domingensis (TD) ranged from 0.3 to 0.4 (over 70% of the biomass below ground). In high nutrient situations SA had a ratio of 1.2 and TD had a ratio of 0.7.A water level competition experiment indicates that SA establishes quicker than TD or S. californicus (SC). However, after one year SA gives way to SC in deeper water (50- 80 em) and maintains dominance in shallower water (10-40 em). TD was the slowest starter and had the lowest percent cover of all three species after one year (24%)

Life History Strategies of California Native Wetland Plants : Implications for Wetland Creation and Restoration

This project focused on obtaining data on life history strategies of wetland plants from the California Central Valley wetlands. We have attempted to obtain comprehensieve information and functional assessment of representative native and exotic wetland plants from inland wetlands of northern California. Thirty four species were selected for assessment of their germination and seedling establishment characteristics. Information on biomass of mature plants together with data on tissue nutrient concentration, species cover, species richness, and soil properties was collected for a set of 22 species throughout the range of twelve Central Valley wetlands. In addition, a controlled experiment including combinations of two water levels and two nitrogen and phosphorus concentrations was conducted using five species

Removal of Herbicide Residua and Nitrates from Agricultural Waters by Aquatic Plants

WRC project W-727 focuses on evaluating the capacity of selected aquatic plant species for low concentrations of herbicide and nitrate removal from nursery waste waters. Two nurseries in the Sacramento area were selected as test sites. From June 1988 through October 1989, water samples from inflow and outflow water from both nurseries were collected and analysed for inorganic constituents and herbicides. Of the herbicides analyzed (simazine, oryzalin, oxyfluorfen and pendimethalin), only oryzalin and oxyfluorten were present in measurable quantities. Pendimethalin was never detected and simazine appeared in detectable quantities only twice. Both nitrate and ammonia nitrogen concentrations were consistently high in outflow from both nurseries, except for the period of about three months during the winter. Soluble reactive phosphorus was relatively low

Selection of Native Wetland Plants for Water Treatment of Urban Runoff

Field sampling was conducted in relatively undisturbed wetlands as well as in wetlands impacted by urban runoff to obtain information on ranges of biomass, nutrients and heavy metals accumulation in different type of common wetland plant species. The above ground biomass of erect emergent macrophytes, tules and cattails, (Scirpus spp., Typha spp.) ranged from 560 g to 3015 g of dry mass per square meter with the average nitrogen concentration of 0.9%. The creeping or soft emergent macrophytes such as water primrose, water cress and pennywort (Ludwigia peploides, Nasturtium aquaticum, Hydrocotyle verticillata, Sagittaria latifolia) usually reached significantly lower biomass (average of about 450 gm-2) but the biomass was richer in nitrogen (3%). Representatives of the second group were also characterized by significantly faster decomposition rates. Methods of propagation of plants from rhizome and stem cuttings were elaborated. A greenhouse experiment carried out to determine the dependence of growth characteristics on water level showed that Hydrocotyle verticillata seemed to be most sensitive to low water levels followed by Nasturtium aquaticum. Ludwigia peploides grew well at all five tested water levels. Both Hydrocotyle verticillata and Nasturtium aquaticum were more sensitive to high nitrogen concentrations than Ludwigia peploides. The mesocosm experiment studying the effect of four different water levels on the growth and biomass allocation in tall erect emergents (Scirpus californicus, S. acutus, Typha domingensis, Phragmites australis) and short emergents (Polygonum sp., Scirpus robustus, Sagitta ria latifolia and Ludwigia peplaides) showed that with the exception of Typha domingensis, Sagitta ria latifolia and Scirpus robustus, all other species allocated more biomass into belowground organs in the low water level treatment than in the high water treatment. Results of this experiment in combination with the observations from the field are crucial for proper species selection for various treatment purposes.Five species, Scirpus californicus, S. acutus, Typha domingensis, Sagitta ria latifoia and Ludwigia peploides, were grown in outdoor hydroponic cultures in a heavy metal experiment. Zinc, lead, cadmium and copper in the concentrations of 0.1, 1 and 10 ppm of were added to the nutrient solution in the cultures. After two weeks of exposure to the heavy metals, plants were measured, harvested, biomass was sorted into roots, rhizomes, stems and leaves, dried and analyzed for concentrations of individual metals. There were no statistically significant differences in the growth expressed as the percentage increment of total length between the control and all concentrations of all metals. However, there were species and organ specific differences in the accumulation of individual metals. Most metals were accumulated in roots, specifically adventitious roots. Ludwigia peploides seemed to be the most efficient in the accumulation of all metals tested

Removal of Herbicide Residua and Nitrates from Agricultural Waters by Aquatic Plants

WRC project W-727 focuses on evaluating the capacity of selected aquatic plant species for low concentrations of herbicide and nitrate removal from nursery waste waters. Two nurseries in the Sacramento area were selected as test sites. From June 1988 through October 1989, water samples from inflow and outflow water from both nurseries were collected and analysed for inorganic constituents and herbicides. Of the herbicides analyzed (simazine, oryzalin, oxyfluorfen and pendimethalin), only oryzalin and oxyfluorten were present in measurable quantities. Pendimethalin was never detected and simazine appeared in detectable quantities only twice. Both nitrate and ammonia nitrogen concentrations were consistently high in outflow from both nurseries, except for the period of about three months during the winter. Soluble reactive phosphorus was relatively low