Responses of fish and macrobenthic assemblages to hydrologic disturbances in Tijuana Estuary and Los Peñasquitos Lagoon,California

Changes in the assemblages of fishes and benthic macro-invertebrates were evaluated in relation to wastewater inflows at Tijuana Estuary and impounded streamflows and mouth closure at Los Peñasquitos Lagoon. Freshwater from sewage spills or winter rains lowered water salinities and had major impacts on the channel organisms of both southern California coastal wetlands. Benthic infaunal assemblages responded more rapidly to reduced salinity than did fishes, with continued salinity reduction leading to the extirpation of most species. Both the fish and benthic invertebrate assemblages became dominated by species with early ages of maturity and protracted spawning seasons. Between-system comparisons showed that good tidal flushing reduced negative impacts on both the fish and benthic assemblages.     

Catastrophic events reveal the dynamic nature of salt-marsh vegetation in Southern California

Recent hydrological disturbances, including flooding, dry-season streamflow, and drought, greatly altered coastal wetland habitats in sourthern California. At Tijuana Estuary, a six-year study of salt-marsh vegetation patterns during these rare conditions documented substantial temporal variability in plant growth and distribution. Important to cordgrass (Spartina foliosa Trin.) dynamics were the amount and timing of streamflows, which reduced soil salinity and alleviated stresses on plant growth. Poorest growing conditions occurred in 1984 when both river and tidal flows were lacking; soils had low moisture and extreme salinities (avg.=104‰ in September). Plant stress was documented in 1984 as high mortality (62% fewer stems than in 1983) and reduced height (19% less than in 1983). Cordgrass height was greatest in 1980 following winter flooding (20% increase over 1979); densities were greatest in 1983 with summer freshwater influxes (60% increase over 1982). A carbon allocation model is proposed to explain the varied responses.     

Freshwater impacts in normally hypersaline marshes

Heavy rainfall in 1978 and 1980 caused flooding of southern California salt marshes. Examination of three marshes demonstrated a broad range of freshwater effects which correlated with the degree of change in soil salinity. At Tijuana Estuary (1980), a short-term reduction in the salinity of normally hypersaline soils was followed by a 40% increase in the August biomass of Spartina foliosa. At Los Penasquitos Lagoon (1978), a longer period of brackish water influence was followed by a 160% increase in August biomass of Salicornia virginica. At the San Diego River (1980), flood flows were augmented by major reservoir discharge. Continuous freshwater flow leached most of the marsh soil salts and caused replacement of halophytes by freshwater marsh species. The first two cases probably fell within the normal range of flooding events, even though the hydrology of both watersheds has been modified. The vegetation response was functional; productivity increased but there was no major change in species composition. As expected, vegetation rapidly returned to preflood conditions. However, the long-term freshwater flow in the Dan Diego River was unnatural. Floral composition changed as soils were leached of salts. Recovery following the return of saline soils has been slow because many native halophytes are not good colonizers. The system's resilience is limited, and modification of natural stream discharge can cause permanent changes in coastal wetlands.     

Damage to cordgrass by scale insects in a constructed salt marsh: Effects of nitrogen additions

Because tall cordgrass (Spartina foliosa) is needed for nesting by the endangered light-footed, clapper rail, managers of constructed salt marshes in southern California are proposing large-scale nitrogen fertilization to improve cordgrass growth. How this might affect an existing infestation of scale insects (Haliaspis spartina) and the degree of damage these insects cause to their cordgrass hosts was unknown. We explored the effects of timing and duration of fertilization onHaliaspis damage to cordgrass, as well as the timing ofHaliaspis dispersal, in a constructed marsh at Sweetwater Marsh National Wildlife Refuge in San Diego Bay, California. Fertilization did not result in increasedHaliaspis abundance. After a large dispersal pulse in late May,Haliaspis establishment in the long-term fertilized plots was greater than in the controls; however, this trend reversed in August, when many more stems in the control plots were infested with large numbers ofHaliaspis. Since adultHaliaspis cannot leave a feeding site, losses of individuals in the fertilized plots were apparently due to mortality, perhaps resulting from mechanical or chemical changes in the fertilized plants or increased predation. Late in the growing season, plots fertilized with 10 applications of urea over 20 wk had the lowest meanHaliaspis abundance. Plots fertilized only in March, April, June, or August did not differ from controls in meanHaliaspis abundance.Haliaspis was never abundant in the fertilized or control plots in the adjacent natural marsh. This study suggests that fertilization, of constructed salt marshes in San Diego Bay may proceed without concern that furtherHaliaspis outbreaks will be facilitated.     

Episodic colonization of an intertidal mudflat by native cordgrass (<Emphasis Type="Italic">Spartina foliosa</Emphasis>) at Tijuana Estuary

Following heavy winter storms and sedimentation in 1993,Spartina foliosa (Pacific cordgrass) clones established on a 6.5-ha mudflat in Tijuana Estuary, with over 80 new clones counted by 1997. El Niño Southern Oscillation (ENSO) storms in 1993 apparently facilitated the habitat conversion through river flooding, which caused a temporary reduction in soil salinity and delivered large volumes of sediment. Extreme sedimentation likely raised mudflat elevations enough to allowSpartina establishment. We hypothesized that clones, once established, increased sedimentation in a positive feedback loop leading to accelerated habitat conversion. We collected data on elevation,Spartina expansion, and sediment accretion in two consecutive years (1998–1999). The elevation range of the mudflats in 1998 (0.5–0.83 m NGVD) was within the elevation range ofSpartina at this site (0.39–0.83 m NGVD), indicating that remaining mudflats are at elevations suitable for further expansion. Sediment accretion ranged from 4.0–12.7 cm between 1997–1998 (ENSO conditions), but was close to long-term averages (? cm yr^?1) in 1998–1999 (nonflood year) indicating how susceptible Tijuana Estuary is to sedimentation from episodic storms. Although accretion rates were similar withinSpartina clones and on bare mudflats over the ENSO winter, clones were typically dome-shaped suggesting higher sediment retention rates within clones. The radial expansion rates of clones (1.31±0.25 m in 1998; 1.12±0.07 m in 1999) approximated the maxima reported for this species and were not related to clone size or vigor. Conditions on the mudflat appear ideal forSpartina growth, masking differences that might otherwise be observed. Given the likelihood of sedimentation-driven habitat conversion in southern California and other Mediterranean-type estuaries, management efforts are needed to address sedimentation issues on a watershed scale. We recommend that wetland restoration projects in southern California include large areas of intertidal mudflat, both to maintain habitat for shorebird feeding and to allow colonization by salt marsh vegetation.     

Mechanical shredding of water hyacinth (<Emphasis Type="Italic">Eichhornia crassipes</Emphasis>): Effects on water quality in the Sacramento-San Joaquin River Delta,California

Management actions to control invasive aquatic species can have significant ecosystem-scale effects. We evaluated the water chemistry and nutrient effects of mechanical shredding to control water hyacinth (Eichhornia crassipes) in an agricultural slough and a tidal wetland on the Sacramento-San Joaquin River Delta, California. Shredding was conducted with two types of shredder boats in fall of 2003 and another boat in spring of 2004. Shredding measurably affected water quality, but specific effects varied as a function of shredding site and season. Significant increases were observed for total Kjeldahl nitrogen and total phosphorus for all experiments. Dissolved oxygen effects varied by site, decreasing after shredding at the agricultural slough but increasing at the tidal wetland. The increase in dissolved oxygen likely resulted from tidal incursions from the adjacent river. A year-long time series of dissolved oxygen data indicated a negative relationship between hyacinth abundance and dissolved oxygen concentrations. Hyacinth contained similar tissue concentrations of mercury to underlying sediments, suggesting that plant harvesting could aid mercury remediation efforts. Simple mass calculations indicated that Delta-wide shredding operations could cause between 0.1% and 9.6% increases in the overall abundance of carbon, nitrogen, and phosphorus in the Delta water column. Results suggest that local effects of management actions to control invasive aquatic plants will vary widely as a function of site-specific hydrology, but that estuary-wide effects would be limited.     

A Method for Installing Piezometers in Large Cobble Bed Rivers

An impact drive point method is described for emplacing piezometers in a cobble river bottom where this has previously been difficult without the use of drilling rigs. To force the drive point piezometers through coble, the vibrational impact of an air-powered hammer was carried directly to the drive point by the use of an internal drive rod. After insertion to depth, the drive rod was removed from the lower portion of the piezometer and a standpipe was added to extend the piezometer above the river level. Piezometers installed in this way have permitted water quality analysis and dynamic measurement of vertical potentials in cobble sediments ranging in size from 2.5 to >30 cm and the method has been successfully used in the Columbia River, USA, and Töss River, Switzerland. This innovative method provides information on the hydrodynamics of pore water in highly permeable, cobble deposits that are common in high-energy river and lake bottoms. Piezometers installed using the internal drive rod method facilitate the assessment of the temporal and spatial dynamics of recharge and discharge at the ground water/surface water interface and analyses of the ecological connectivity between the hyporheic zone and surface water of rivers and streams. This information will lead to improved management decisions related to our nation's ground water and surface water supplies.     

Grassroots social innovations and food localisation: An investigation of the Local Food programme in England

This paper seeks to orientate research on local food networks more firmly towards ideas of grassroots and social niche innovations. Drawing on recent conceptual ideas from strategic niche management, this paper provides an exploratory analysis of attempts to spread grassroots social innovations through the Big Lottery Local Food programme run by the Royal Society of Wildlife Trusts in England. This £ 59.8 million programme aims to distribute grants to a variety of food-related projects and to make locally grown food more accessible and affordable to local communities. Insights into 29 funded projects, of varying length and scale of operation, are provided through over 150 telephone and personal interviews. While the Local Food programme is undoubtedly about bringing small, often neglected pieces of land into production and increasing access to affordable food, results show that the programme is also very much seen as a vehicle for building community capacity through facilitating community cohesion, healthy eating, educational enhancement and integrating disadvantaged groups into mainstream society and economy. The paper concludes with some reflections on the extent to which the concept of grassroots social innovations, as a form of niche innovation, can help understand the ability of local food networks to develop the capacity of communities to respond to locally identified problems and to effect more widespread, sustainable change.     

Defining the distribution of arsenic species and plant nutrients in rice (Oryza sativa L.) from the root to the grain

The transport mechanisms of As from contaminated soil or irrigation water into roots and subsequently into grain, and the As species distribution—a toxicity determinant, is critical for assessing health risks imposed by As. However, the commonly-employed extraction of plant material with trifluoroacetic acid (TFA) has not proven successful in preserving inorganic As species. Synchrotron-based spectroscopic techniques are useful for discerning elemental distributions and chemical speciation of elements in situ. Here, we both characterize the mineral phases of Fe coatings on rice roots, and quantify plant nutrients and As species in situ on roots and grain samples. Arsenic in rice grains was present in bran layers as oxidized As (69-88% as As(V)_i and 12-31% as DMA) and in the germ as a mixture of As(V)_i and As(III)_i, but was non-detected from the endosperm, which is consistent with previous findings. The extent of Fe coatings on rice roots was variable and, when present, consisted of lepidocrocite (γ-FeOOH), goethite (α-FeOOH) and ferrihydrite (Fe(OH)₃·nH₂O). Arsenic was co-located with root Fe coatings, but our findings indicate that Fe is not a direct interceptor of As uptake, and is rather a bulk scavenger mostly near the air-water interface. On whole root mounts with Fe plaque, arsenic was present as mixed species of As(V)_i (44-66%) and As(III)_i (34-56%). Within a root cross-section, oxidized As species were dominant in the xylem (86% as As(V)_i and 14% as DMA) whereas mostly reduced species (71% as As(III)_i, 29% as AsGlu₃) resided within a vacuole adjacent to the xylem. This finding contrasts the prevailing view that As(V)_i is rapidly reduced in roots and transported to shoots as As(III)_i, and points to the importance of interspecies differences in As-uptake dynamics.     

An analysis of Apollo lunar soil samples 12070,889, 12030,187, and 12070,891: Basaltic diversity at the Apollo 12 landing site and implications for classification of small‐sized lunar samples

Lunar mare basalts provide insights into the compositional diversity of the Moon's interior. Basalt fragments from the lunar regolith can potentially sample lava flows from regions of the Moon not previously visited, thus, increasing our understanding of lunar geological evolution. As part of a study of basaltic diversity at the Apollo 12 landing site, detailed petrological and geochemical data are provided here for 13 basaltic chips. In addition to bulk chemistry, we have analyzed the major, minor, and trace element chemistry of mineral phases which highlight differences between basalt groups. Where samples contain olivine, the equilibrium parent melt magnesium number (Mg#; atomic Mg/[Mg + Fe]) can be calculated to estimate parent melt composition. Ilmenite and plagioclase chemistry can also determine differences between basalt groups. We conclude that samples of approximately 1–2 mm in size can be categorized provided that appropriate mineral phases (olivine, plagioclase, and ilmenite) are present. Where samples are fine‐grained (grain size <0.3 mm), a “paired samples t‐test” can provide a statistical comparison between a particular sample and known lunar basalts. Of the fragments analyzed here, three are found to belong to each of the previously identified olivine and ilmenite basalt suites, four to the pigeonite basalt suite, one is an olivine cumulate, and two could not be categorized because of their coarse grain sizes and lack of appropriate mineral phases. Our approach introduces methods that can be used to investigate small sample sizes (i.e., fines) from future sample return missions to investigate lava flow diversity and petrological significance.