The Arbuckle series contains gravel in banded patterns suggesting the edge of a flood plain subject to major high energy events alternating with low energy events. The soils are well drained, formed on terraces in semi-consolidated alluvium derived from igneous and sedimentary rocks. The soils are used for irrigated field crops, pasture, and dryfarrned grain. The Elkhorn and Elkhorn variant series are among the oldest series in the entire slough. They are derived from the Aromas Red Sands and have a well developed argillic horizon. The soils are on marine terraces and dune-like hills, underlain by weakly consolidated sandy sediments or ferruginous sandstone. Permeability is moderately slow, although the Elkhorn Variant is slow. The argillic horizon has a low porosity, thus water tends to flow laterally in contact with this horizon. The soils are used for Brussels sprouts, strawberries, artichokes, broccoli, annual pasture, hay, or rangeland.It is formed on hill and uplands in old marine sand dunes or in material weathered from soft sandstone. These soils are somewhat excessively drained. There is no argillic horizon. They are most often used for range, wildlife habitat and watershed, with some orchard, row crops, and Christmas trees. We measured seven sediment fans at the base of strawberry roads and paths around the Central Marsh, and estimated they contained 3,745 ft.3 of deposited sediments. The Central Field is approximately 8.8 acres, for an average of 426 ft3/acre,grow bag for tomato deposited sediments. The sediment fans we measured consisted mostly of the heavier sand fraction. Any eroded clays and soil organic matter were not deposited in the fans and were likely carried into the marsh, possibly along with some portion of the heavier sand fraction. We initiated sampling of deposited sediment fans during winter 1993-1994 as a survey technique to help us gain a better understanding of the contribution of surface run-off to nutrient loading in the marshes.
Sediment transport from the strawberry fields occurs whenever there is rain or irrigation, and the amount of sediment carried depends on soil moisture content, time since last rain or irrigation event, rate and total amount of rainfall, time since cultivation, size of berry plants, plus the type and extent of erosion control practices implemented by the growers. While much of the run-off and the finer fractions of suspended sediments ultimately make their way to the marshes, a substantial portion of the coarser sediments are deposited in fans at the bases of field roads along the marsh margins. However, because of the relationships of N and P compounds to water and clay particles, our estimates of the nutrient load in deposited sediments are surely very low in relation to the total amounts of these nutrients entering the marshes. Our results show that nutrient loading in transported sediments is highest at the beginning of the winter rainy season for N03, NH4, and labile P. We did not collect samples from sediment fans deposited after the initial rain events of the season . But based on these numbers from slightly later in the season, we hypothesize that nutrient loading is highest during the first rain events after planting. There are several reasons for this. One is the presence of fertilizer nutrients in freshly cultivated and fumigated soils in the absence of plants with big enough root systems to take up those materials. Establishment of the plants and increased nutrient uptake later in the winter when the later samples were collected may account for decreased levels of N and P in sediments at those times. Enhanced levels of N and P in early winter run-off may also originate from a soil reservoir of fertilizer-applied nutrients applied in years past which are made available by the turning under of the crop and the intense cultivation of the soil prior to fumigation and planting. Lower levels of sediment Nand P later in the rainy season may also reflect a net movement of these nutrients into the wetlands. The macro-vegetation of the mudflat zone consisted of blue green algae, Enteromorpha spp., and Rupia maritima . Blue green algae formed extensive floating mats at three of the four sites. Enteromorpha, not yet identified to species, also formed floating mats and was only absent at one site. Ruppia, an aquatic herb, was present in the Central Marsh but only abundant in the southern marsh. Vegetation in the mid-Pickle Weed zone was dominated by Salicornia, but there were less common species present.
The estimated cover in the transects was 100% Salicornia. There was some variability in the height of Salicornia between sites, but the color was consistently green . Other species noted in this zone included: Atriplex leucophylla , Cuscuta salina, Frankenia grandifolia, Jaumea carnosa, Distichlis spicata, and Elymus sp. The transects through the marsh-field border found a gradient from salt marsh species dominated by Salicornia virginica, Distichlis spicata, and Cuscuta salina to a more species-rich border flora with a maximum of 14 species. The species found are typical of wetland-upland transition zones along the central California coast. The coast line of California contains several distinct vegetation types which are related to the topography, hydrology, soil type, latitude, historical land use patterns, and disturbance regimes. The Azevedo Ranch is in the midst of five vegetation communities: Coastal salt marsh, California annual grasslands, maritime chaparral, north coastal scrub and live oak woodland. The marshes harbored a restricted fauna, relative to the fauna found in the adjoining slough . The South Marsh showed the lowest abundance and diversity, with almost no living macrofauna collected from the benthos. This marsh undergoes the most dramatic changes in water chemistry during the year . In addition, the sediment in the central portion of this marsh was completely anoxic. The Central Marsh likewise showed few infaunal invertebrates. This may also be a reflection of the changeable water quality and anoxic sediments. The North Marsh showed the greatest abundance and diversity infaunal invertebrates of the three Azevedo marshes. This is consistent with the greater flushing of this marsh with tidal water. The distribution of infaunal invertebrates within the three marshes tracks the relative degree of disturbance in each. The least flushed, most disturbed marsh showed no infauna while the largest, best flushed and least disturbed marsh showed the greatest diversity. All of these marshes exhibited a restricted fauna relative to the control pond on the Reserve. Future sampling will examine more of the seasonal changes associated with these ponds and will work to link land use practices with the health of the infauna. The 1 acre South Marsh is the smallest of the three and is cut off from tidal exchange . It has experienced the greatest degree of filing from the adjoining agricultural operations and is surrounded by the smallest buffer of salt marsh. This pond had a growth of Ruppia maritima in July, 1992 that was heavily encrusted with consolidated sediment, perhaps cemented by a bacteria or protozoan. This mat of Ruppia formed a false bottom in the pond above which were pupae of the brine flies and corixid beetles. The underlying sediment was completely anoxic and no living infauna were retrieved from the cores in 1992. The summer 1993 samples contained one oligochaete and several corixid beetles. Again,grow bag for blueberry plants the sediments were completely anoxic, although the Ruppia canopy was not present.
The Central Marsh is 4.1 acres in extent and is intermediate in size and disturbance . The central pond is blocked from tidal action by high culverts and by a low berm across the mouth of the marsh . This marsh also receives direct freshwater input during the rainy season from a culvert draining an agricultural pond above the road. Sediments in this pond were oxidized on the surface, but anoxic a few millimeters below the surface. The infauna reflected these difficult conditions and few species were recovered from either station on either sampling date. The North Marsh is the largest of the three at 10.1 acres . It is connected to the main channel of the slough through two culverts, one at either end of the marsh. This marsh receives the most tidal flushing, though the central portions of the marsh are not well flushed. In all cases, the North Marsh showed the greatest number and diversity of infaunaI species of the three Azevedo marshes. Samples taken in July 1993 showed an absence of many of the soft-bodied species collected in October of 1992. In addition, the presence of a podocopid ostracod in July was notable. Many dead ostracods and shells were recovered from these samples. In some areas, evidence of anoxic waters and sediments was observed, and dead ostracod shells found. The control pond on the National Estuarine Research Reserve served as a contrast to the Azevedo marshes. It is more fully flushed, has never been cultivated, and is undisturbed relative to the Azevedo marshes. Infaunal samples showed greater species diversity in this pond relative to the Azevedo marshes. The invertebrate community in the control pond was more similar to that found in the main channel of the slough than the Azevedo marsh .community. Methyl bromide is a soil fumigant of environmental concern because of its high potential to deplete stratospheric ozone . A treaty signed by 160 nations of the United Nations Environment Program regulates the stepwise decrease of MeBr consumption to a complete phase-out by January 2005 for developed countries and by 2015 for developing countries . The stringent regulations limiting the use of MeBr prior to its complete phase-out stimulated the search for alternative fumigants because soil fumigation remains a central tool in strawberry production. For the past 45 years, preplant fumigation of agricultural soils with a combination of MeBr and chloropicrin has been a reliable and effective tool to control soil borne pathogens, nematodes and weeds in many vegetable, fruit, nuts and nursery crops worldwide. The irritant compound CP is added to the odorless MeBr as a warning agent to reduce the risk of accidents during soil fumigation and because of the synergistic biocidal effect of these two chemicals on soil pathogens . The elimination of MeBr could severely impact growers and farmers in the United States and the Mediterranean region . In continuous strawberry production systems, the soil may host many deleterious nematodes and pathogens such as Phytophtora cactorum, P. fragariae, Verticillium dahliae and Colletotrichum acutatum. In California, where 80% of US strawberries are grown, MeBr + CP combinations effectively control wilt disease , thus playing a crucial role in commercial strawberry production. Currently, there are several available alternatives to MeBr, including an emulsifiable concentrate of CP and 1,3-dichloropropene . Applied alone, CP has high biocidal activity against fungal pathogens but is not as effective as MeBr against weeds and nematodes. Another viable alternative is 1,3-dichloropropene , which is an effective nematicide but has relatively low activity against fungi and weeds . To broaden its biocidal activity, 1,3-D can be combined with chloropicrin as found in various combinations such as InLine . In addition, several experimental chemical alternatives are being studied for their efficacies against pathogens and pests. Iodomethane can be as effective as MeBr, and it is not as likely to deplete ozone because Midas is photolyzed before it reaches the stratosphere . The dilution of Midas with CP can decrease costs for this fumigant and increase efficacy due to synergy with CP . Another experimental chemical alternative is propargyl bromide , which was developed during the 1960s. Although, PrBr demonstrated potential as a viable MeBr replacement it was never registered due to its highly explosive character . With the development of a stabilized formulation of PrBr, research interest in this compound as a soil fumigant has increased recently. Studies have been conducted to determine the biological degradation of various fumigants in soil and their efficacies against soilborne pests and weeds relative to MeBr + CP combinations . Fumigants are among the pesticides with notable effects on soil microorganisms because of their broad biocidal activity . The high biocidal activity of fumigants may cause a “biological vacuum” and increase pathogen re-colonization. Kandeler et al. suggested that the composition of the microbial community strongly affects the potential of a soil for enzyme-mediated substrate catalysis. Consequently, changes in microbial diversity in fumigated soils may also reduce microbial functionality.