Water hyacinth (Eichhornia crassipes) is an invasive species that has modified ecosystem functioning in the Sacramento-San Joaquin Delta (Delta), California, USA. Studies in lakes and rivers have shown that water hyacinth alters water quality. In tidal systems, such as the Delta, water moves back and forth through the water hyacinth patch so water quality directly outside the patch in either direction is likely to be impacted. In this study, we asked whether the presence or treatment of water hyacinth with herbicides resulted in changes in water quality in this tidal system. We combined existing datasets that were originally collected for permit compliance and long-term regional monitoring into a dataset that we analyzed with a before-after control-impact framework. This approach allowed us to describe effects of presence and treatment of water hyacinth, while accounting for seasonal patterns in water quality. We found that although effects of treatment were not detectable when compared with water immediately upstream, dissolved oxygen and turbidity became more similar to regional water quality averages after treatment. Temperature became less similar to the regional average after treatment, but the magnitude of the change was small. Taken together, these results suggest that tidal hydrology exports the effects of water hyacinth upstream, just as river flow is known to transport the effects downstream, creating a buffer of altered water chemistry around patches. It also suggests that although water hyacinth has an effect on dissolved oxygen and turbidity, these parameters recover to regional averages after treatment.

Many estuarine ecosystems and the fish communities that inhabit them have undergone substantial changes in the past several decades, largely due to multiple interacting stressors that are often of anthropogenic origin. Few are more impactful than droughts, which are predicted to increase in both frequency and severity with climate change. In this study, we examined over five decades of fish monitoring data from the San Francisco Estuary, California, USA, to evaluate the resistance and resilience of fish communities to disturbance from prolonged drought events. High resistance was defined by the lack of decline in species occurrence from a wet to a subsequent drought period, while high resilience was defined by the increase in species occurrence from a drought to a subsequent wet period. We found some unifying themes connecting the multiple drought events over the 50‐yr period. Pelagic fishes consistently declined during droughts (low resistance), but exhibit a considerable amount of resiliency and often rebound in the subsequent wet years. However, full recovery does not occur in all wet years following droughts, leading to permanently lower baseline numbers for some pelagic fishes over time. In contrast, littoral fishes seem to be more resistant to drought and may even increase in occurrence during dry years. Based on the consistent detrimental effects of drought on pelagic fishes within the San Francisco Estuary and the inability of these fish populations to recover in some years, we conclude that freshwater flow remains a crucial but not sufficient management tool for the conservation of estuarine biodiversity.

Tobias, V.D. and Nyman, J.A., 0000. Leaf tissue indicators of flooding stress in the above- and belowground biomass of Spartina patens. Many factors, such as rising sea levels and human alterations, threaten coastal wetlands in the United States and around the world. To reverse some wetland loss, dredge material, tidal flow, or river flow can be used to create new wetlands, or existing wetlands can be managed to increase plant productivity. Identifying the causes of limited production can improve management plans by suggesting possible remedies. Managing and restoring marshes depends on understanding which stress factors limit growth of key marsh-building plants. Spartina patens is a common marsh-building species of grass in brackish marshes along the Gulf of Mexico and Atlantic coasts of North America, and it is often the target of management and restoration plans. Spartina patens was grown under six flooding levels in a field experiment. Spartina patens plants grown at lower elevations had cons...

Elemental concentrations in leaf tissue can identify limiting conditions in crops and can be useful in managing and restoring marshes. Coastal management and restoration plans frequently include Spartina spp. because they are common plants in coastal wetlands across North America. Researchers frequently compare results of stoichiometric studies among Spartina spp. to corroborate results, although their stoichiometry may not be comparable. We compare the stoichiometry of paired samples of Spartina patens and Spartina alterniflora collected across Louisiana. Overall differences in stoichiometry between species, seasonal changes, and effects of porewater chemistry were quantified. Manganese (Mn) concentrations and calcium (Ca) concentrations were higher in S. alterniflora and the difference in [Ca] increased seasonally. Sodium concentrations were similar, except during prolonged inundation. Short flooding durations decreased carbon (C):nitrogen (N) without increasing [Mn] or flooding stress in both species.

Decisions about whether to designate a species for conservation and protection depend on the ability to summarize their population trajectories and their risk of extinction. Such decisions may rely on quantitative population viability analyses based on a time series of abundance index values that are derived from a monitoring program. In the case of the Longfin Smelt (Spirinchus thaleichthys), a decision to protect a distinct population segment of the species under the U.S. Endangered Species Act was informed by several indices of population abundance. In this paper, we combined individual population viability analyses into a single metric for extinction risk using a meta-analysis framework. Individual monitoring surveys for this species generally agreed that the trajectory of abundance was downward, but variation introduced uncertainty. Combining data from several surveys produced a better summary of the population growth rate. We also used the population growth rates in a simulation to estimate the probability that the abundance of Longfin Smelt dropped too low to recover. We found that this probability of quasi-extinction was substantial, exceeding 20 % over two decades. This study demonstrates a practical way that having multiple sources of information creates better information about the trajectory of a population. Individually, the surveys contribute information about specific life stages or ages to our understanding of the population. Combined into one metric and an associated graphical summary, this analysis succinctly communicates risk and creates a benchmark for evaluating future management decisions.