We also became interested in focusing on the vegetated borders between the pocket marshes and the cropland as a potential means to reduce the soil-water nutrient content before it entered the marshes. Therefore, in year two, the lysimeters were moved to the uplands/wetlands interface, at the border of the cropped area. Stations consisting of four lysimeters placed at the two foot depth, one meter apart from one another, were placed at four locations in the field. Two stations were placed at the bottom of roadways, where surface flow is concentrated, and two stations were placed where there were no roads and surface flow was minimized. During sampling times, vacuums were drawn using a hand pump and left overnight. Water samples were collected the next day and nitrate-N levels measured on the same day in the lab using a selective nitrate ion probe. Sub-samples were frozen and later analyzed for nitrate-N using a spectrophotometer. .Samples were collected approximately monthly from January to June 1993, with a final sample in August. During 1994, samples were collected twice-monthly, from January to April. These 1994 samples were also analyzed for ammonium-nitrogen and phosphorous content. In 1993, grassland soils dried up by mid-June so no samples could be collected. Grassland samples were not collected in 1994. The pocket marshes on the Azevedo property are separated from the slough by a railway dike ,25 litre plant pot and water exchanges between the slough and the pocket marshes through culverts under the dike. We call the marshes South Marsh, Central Marsh, and North Marsh. The heights of the culverts varies and there is a gradient of flushing and size with the North Marsh being the largest and best flushed and the South Marsh being small and having little if any connection to the tidal waters. The Central Marsh is intermediate in size and flushing with some input from a perched freshwater pond at the upland end of the marsh.
The pocket marshes were added as sample sites to a hydrological monitoring program that has been sampling surface water at 21 stations around the slough since 1988 . Once each month we monitored water temperature, salinity, oxygen, turbidity using a Nephelometer, pH, phosphate, nitrate, and ammonium. Water in the pocket marshes was sampled from the 0.5 m depth without disturbing sediments. Water chemistry analyses were conducted by the Monterey County Water Resources Agency . Hydrologists developed contour maps of the marshes which established limits of pickleweed and upper limits for the potential restoration of tidal action. Characterization of the vegetation entailed the use of line intersect, point intersect, and quadrat methods. The sampling was stratified based on vegetation patterns. Vegetation was sampled in the upper mudflat zone, midPickle Weed . During one hour observation periods, all waterbirds present were counted using binoculars and a lOx spotting scope. Birds were observed from the railroad berm at five to eight feet above marsh level and 10 to 100 meters distant. Detailed results are reported in a senior thesis by Neuman and Hickey. Although strawberries are a perennial plant, they are treated as an annual in most coastal California strawberry growing areas. Because of the marginal nature of Elk hom Slough soils for fanning, strawberry culture in the region is generally done on a two-year cycle in order to avoid the expense of replanting every year. Field preparation begins in September when irrigation systems are removed and fields are ripped and chiseled in preparation for whole-field fumigation with a mix of methyl-bromide and chloropicrin. Fumigation destroys soil pathogens, weed seeds, and most soil biota. After fumigation, beds and furrows are formed and planting in raised beds begins in mid-October or November. Varieties used were Selva and Seascape. Harvest begins in March! April and continues until fall.
Plants left in the ground for a second harvest season yield a berry that is smaller and softer, and these fruits are generally not fresh-marketed but used for processing. The Azevedo Ranch is divided into two agricultural leases. Mr. C. directly leases the South Field, and Mr. S. subleases the central and North Fields from a shipping firm which also functions as a lender. Both leases were planted in fall 1991, including fumigation, and again in fall 1993. Mr. C. leases 30 acres and has leased that plot for 7 years. Mr. S. farms a total of 64 acres, with 10 acres planted with cv. Seascape, and the remainder in cv. Selva. Mr. S. farms a total of 357 acres of strawberries in the Elkhorn Slough watershed, and this was his first crop on the Azevedo property. Prior to and during the harvest season, applications of insecticides, miticides, and fungicides are made on a regular basis, in a cycle sometimes called pick and-spray. Harvest crews work from one end of the field to the other, and sometimes they are still finishing up picking when the spray crew starts its work at the opposite end of the field. Mr. C. utilizes a tractor to apply pesticides, which is more typical of practices in the watershed, while Mr. S. uses farm laborers to apply pesticides by hand using hoses connected to a tank truck. Plants are fertilized with controlled-release fertilizer applied at plant-out. The analysis of fertilizer applied on the north and Central Fields at plant-out in 1993 was 18% nitrogen , 8% available phosphorous, and 13% soluble potassium. Mr. S. applies this material by hand to the surface of the beds, down the center, while Mr. C. drills the material into a slot in the center of the beds so that it is buried. In January 1993, Mr. S. applied granular 6-20-20 by hand to the top of the strawberry beds. In January 1994 he applied ammonium sulfate in the same fashion, at the rate of about 80 pounds per acre . Both growers apply nitrogen through the drip irrigation system during the summer.The Elkhorn Slough area is extremely active and has been subject to large scale changes over geologic time. Hydrologically, the area may have been a flood plain for one of the largest rivers in Pleistocene California. More recently, the area has been subject to continued changes in land-use patterns and vegetation cover due to human influences.
The Azevedo Ranch lies within the Salinian Composite Terrane, which is bound by the San Andreas Fault to the east and the Sur-Nacimiento Fault Zone to the west. It is unrelated to contiguous terranes, suggesting that it has migrated from its presumed origin 1500 km to the south . The basement rocks consist of quartz-di orite-ganodio rite rock which are Precambiam to late Mesozoic. In the early Pleistocene the lower reaches of Elkhorn Slough and Elkhorn Valley appear to have been part of a large riverine system draining the Santa Clara Valley and/or the California Central Valley . In the late-Pleistocene the watershed area for the Elkhorn Valley was tectonically truncated,30 litre plant pots bulk substantially reducing the volume of water moving through to the ocean and limiting the flushing and scouring of Elkhorn Valley. During the most recent glaciation event 16,000-18,000 years B.P., a channel over 29 m below present day sea level was cut through the slough. As the earth’s temperatures rose and sea-level began to rise, this channel was flooded. The sediments in the slough are characterized by a finer texture size as one approaches the top of the sediment layers from below where non-marine gravels dominate. During the past 5,000 B.P. until 1946, salt marshes developed along landward margins of the slough. These marshes reduced the energy of the water, allowing further sedimentation and development of marsh vegetation toward the axis of the slough. This is the process by which the Azevedo Ranch pocket marshes were created. Until 1946 the slough was a shallow, quiet-water embayment with restricted tidal action. In 1947 Moss Landing Harbor was built, opening the Elkhorn Slough to direct tidal action. The effect was rapid and dramatic, and today erosion of wetland habitat in the slough continues to be a major concern . There are three main land formations from which the major soil types have been derived: aeolian or colluvian Aromas Red Sands, wave cut terraces, and alluvial sand, silts, and clays. The mapped soils and their classifications are listed in Table 1. Several soil pits made in the terrace and Central Field suggest much greater diversity in soil types and origins on the Azev-vlo Ranch. Many seeps have been observed, where ground water surfaces through soil discontinuities or is forced to the surface by impermeable boundaries. Furthermore, a thick clay layer devoid of sands was found on the slopes of the marshes, suggesting lake deposited clays in a time of slower moving water. The discontinuity of the marine terrace sandstone indicates that it has been eroded by water draining from the uplands. The Alviso series is alluvial consisting of fine texture sizes. The soils have a great deal of organic matter, and unless artificially drained can be almost completely anaerobic below the soil surface. These soils are dominated by wetland plants, Salicornia virginica and Distichlis spieata. This soil encompasses the pocket marshes and their margins, including the area presently farmed. These are considered to be relatively young soils. The soil survey map for the Azevedo Ranch shows Arbuckle gravely loam on the terrace between the north and Central Field. 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. The Arnold series is also considered one of the older soils in the slough. 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, 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.