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Open Access Publications from the University of California

Scholarly Works (10 results)

  • Article
  • Peer Reviewed
UC Davis Previously Published Works (2016)
This study compares soluble phenolics and lignin content in two wetland macrophytes with contrasting life strategies grown under a varying nutrient supply in the field and in a greenhouse experiment. The differences are explained in terms of the protein competition model (PCM) hypothesis relating changes in secondary metabolites to changing nutrient limitation. The two study species, Eleocharis cellulosa (EC) and Typha domingensis (TD), are both widespread in tropical and subtropical freshwater and brackish marshes of the New World, and are often found in P-limited rather than N-limited conditions. TD is a fast-growing competitor with large nutrient requirements. EC is a stress tolerator, quite well adapted to growth in nutrient-limiting environments. In both species, the concentration of phenolics was negatively correlated with increasing growth (due to increasing nutrient levels). This is in agreement with the PCM hypothesis, which predicts an increase in phenolic synthesis when protein synthesis (and consequently growth) is low due to limited resource availability. An interesting difference was found in the correlation between tissue nutrients and phenolics. TD from both the field and the greenhouse showed a negative correlation between tissue P and phenolics, while EC displayed a significant negative correlation between tissue N and phenolics. EC is adapted to low P, and increased tissue P content represents luxury consumption (uptake of P for storage) which is not reflected in increased growth and thus is not correlated with phenolics. These are the first steps in elucidating the relationship among nutrient availability, growth and phenolic content in two important primary producers of tropical and subtropical marshes.
    Cover page: Phenolic content and growth of wetland macrophytes: Is the allocation to secondary compounds driven by nutrient availability?
    • Article
    Technical Completion Reports (1997)

    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%).

      Cover page: Potential of Long-lead Streamflow and Drought Forecasting in California
      • Article
      Technical Completion Reports (2000)

      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.

        Cover page: Life History Strategies of California Native Wetland Plants : Implications for Wetland Creation and Restoration
        • Article
        Technical Completion Reports (1990)

        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.

          Cover page: Removal of Herbicide Residua and Nitrates from Agricultural Waters by Aquatic Plants
          • Article
          Technical Completion Reports (1995)

          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.

            Cover page: Selection of Native Wetland Plants for Water Treatment of Urban Runoff
            • Article
            • Peer Reviewed
            UC Davis Previously Published Works (2009)
            In order to determine the impact of nutrient enrichment on phosphorus (P) limited wetlands, we established experimental P additions in marshes throughout northern Belize. P significantly increased macrophyte primary production, which led to the rapid elimination of cyanobacterial mats. The replacement of cyanobacterial mats by macrophytes constrained autotrophic nitrogen (N) fixation, increased the quantity, and changed the quality of organic matter input to the sediments. We predicted that the activity of sediment heterotrophic N fixers will be impacted by these alterations in carbon input. We used the acetylene reduction technique to measure potential (glucose amended) nitrogenase activity (NA) in sediments from controls and treatment plots that have been P enriched for four years and dominated either by Eleocharis cellulosa, or Typha domingensis for two years. NA in P-enriched plots was 2–3 orders of magnitude higher than NA in controls. NA was positively correlated with the soil reactive P, both total organic and microbial carbon, live root biomass, and total phospholipid fatty acids (PLFA) as an indicator of active microbial biomass. It was negatively correlated with the concentration of ammonium-N. Path analysis revealed that the indirect effect of P on NA through the root biomass was more important than the direct effect of P. NA of the upper sediment layer was consistently higher in Eleocharis than in Typha dominated plots, despite the higher litter input by Typha. We feel that the higher levels of lignin and phenolics occurring in Typha litter, relative to Eleocharis, constrained NA in Typha plots.
              Cover page: Heterotrophic nitrogen fixation in oligotrophic tropical marshes: changes after phosphorus addition
              • Article
              • Peer Reviewed
              UC Davis Previously Published Works (2010)
              Oligotrophic, phosphorus (P) limited herbaceous wetlands of northern Belize are being impacted by P loading from fertilizer runoff. P enrichment causes a shift in autotroph communities from a microphyte (cyanobacterial mats, CBM) to macrophyte (Eleocharis spp., Typha domingensis) dominated system. To document potential effects of P, salinity, and macrophyte species on the heterotrophic microbial community nutritional status (represented especially by specific phospholipids fatty acids and specific respiration rate), biomass and activities, we took soil samples from established P enrichment plots in replicated marshes of two salinity levels. P addition increased microbial biomass carbon (C), nitrogen (N) and P, as well as soil nutrient transformation rates (nitrogenase activity, N mineralization and immobilization, methanogenesis). The effect of plant species (Eleocharis vs Typha sites) was generally lower than the effect of P addition (CBM vs Eleocharis sites) and was most evident at the low salinity sites, where Eleocharis dominated plots had enhanced nitrogenase activity and P microbial immobilization. Salinity reduced the overall rates of microbial processes; it also weakened the positive effect of both P addition and plant species on microbial activities. Lastly, the amount of N stored in microbial cells, likely in form of osmoprotective compounds, was enhanced by salinity.
                Cover page: Heterotrophic microbial activities and nutritional status of microbial communities in tropical marsh sediments of different salinities: the effects of phosphorus addition and plant species
                • Article
                • Peer Reviewed
                UC Davis Previously Published Works (2018)
                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.
                  Cover page: Heterotrophic N2-fixation contributes to nitrogen economy of a common wetland sedge, Schoenoplectus californicus
                  • Article
                  • Peer Reviewed
                  UC Davis Previously Published Works (2018)
                  Different functional groups of macrophytes vary in their impact on aquatic ecosystem structure and processes. The introduction of new species with different growth form, combined with a stochastic event, may have serious and irreversible consequences on lake functioning. Our goals were to document and explain physical, chemical, metabolic and biotic changes in the littoral zones of a volcanic lake before and following two coinciding events: invasion by a submersed macrophyte, Hydrilla verticillata (Hydrocharitaceae), followed by a rapid increase in the lake water level (>2.5 m). We recorded plant biomass, plant tissue C:N:P stoichiometry, macroinvertebrates, water characteristics data along transects through littoral zones, and measured gas emission in controlled mesocosms and in the lake. The native emergent species, Schoenoplectus californicus (Cyperaceae), was generally not able to survive such a rapid water level increase, and Hydrilla spread and formed dense mats further preventing Schoenoplectus regeneration. The impact of another introduced species, the free-floating Eichhornia crassipes (Pontederiaceae), was more localised, despite its much longer presence at the lake. Although the three species had comparable standing biomass, the two invader species had lower C:N:P ratios than Schoenoplectus, resulting in faster decomposition rates and indicating potential shifts in nutrient cycling within the ecosystem. The oxygen profile of the water column was altered by the non-native species in a significantly different manner: in Eichhornia, the saturation concentrations dropped down to 30%–50% of dissolved oxygen, while oxygen supersaturation was recorded in Hydrilla. Both Schoenoplectus and Eichhornia patches exhibited comparable carbon dioxide (CO2) fluxes, sequestering 230 and 300 mg CO2 m−2 hr−1, respectively, during the day and emitting 250 and 200 mg CO2 m−2 hr−1, respectively, during the night. Contrary to these two species, Hydrilla patches sequestered CO2 during the day (34 mg CO2 m−2 hr−1) and night (44 mg CO2 m−2 hr−1). The invasive species maintained a richer community of macroinvertebrates compared to several native species (excluding Schoenoplectus), both in taxa diversity and in numbers of individuals. When the results are considered in the regional context, an increase in nutrient supply could lead to the dominance of free-floating plants. We discussed management options more broadly considering the negative impacts of introduced species balanced against their beneficial effects, in the context of environmental changes.
                    Cover page: Regime shift in the littoral ecosystem of volcanic Lake Atitlán in Central America: combined role of stochastic event and invasive plant species
                    • Article
                    • Peer Reviewed
                    UC Davis Previously Published Works (2020)
                    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 (1μg/L), and over 60% of source water samples exceeded USEPA guidelines for children and immunocompromised individuals. 50% of households reported sole use 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.
                      Cover page: Harmful Algal Blooms Threaten the Health of Peri-Urban Fisher Communities: A Case Study in Kisumu Bay, Lake Victoria, Kenya
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