Meadow Sediments Research Articles

Cool, wet conditions late in the Younger Dryas in semi-arid New Mexico

A thick alluvial sequence in central New Mexico contains the Scholle wet meadow deposit that traces upstream to a paleospring. The wet meadow sediments contain an abundant fauna of twenty-one species of freshwater and terrestrial mollusks and ten species of ostracodes. The mollusks and ostracodes are indicative of a local high alluvial water table with spring-supported perennial flow but without standing water. Pollen analysis documents shrub grassland vegetation with sedges, willow, and alder in a riparian community. Stable carbon isotopes from the wet meadow sediments have δ13C values ranging from −22.8 to −23.3‰, indicating that 80% of the organic carbon in the sediment is derived from C3 species. The wet meadow deposit is AMS dated 10,400 to 970014CyrBP, corresponding to 12,300 to 11,100calyrBP and overlapping in time with the Younger Dryas event (YD). The wet meadow became active about 500yr after the beginning of the YD and persisted 400yr after the YD ended. The Scholle wet meadow is the only record of perennial flow and high water table conditions in the Abo Arroyo drainage basin during the past 13ka.

Groundwater flow and storage within an alpine meadow-talus complex

Abstract. The different types of geological deposits and rock formations found in alpine watersheds play key roles in regulating the rate and timing of runoff to mountain rivers. Talus and alpine meadows are dominant features in these areas, but scant data exist for their capacity to store and transmit groundwater. To gain further understanding of these processes, we have undertaken a combined geophysical and hydrological study of a small (2100 m2) alpine meadow and surrounding talus within the Lake O'Hara watershed in the Canadian Rockies. Several intersecting ground-penetrating radar (GPR) and electrical resistivity tomography (ERT) profiles and a seismic refraction profile were acquired to map the thickness of the talus and to image the topography of the bedrock basin that underlies the meadow. From analysis of the GPR and seismic profiles, we estimate that the talus deposits are relatively thin (<6 m). Combined interpretations from the GPR and ERT data show that the fine-grained sediment comprising the meadow basin has a total volume of ca. 3300 m3 and has a maximum thickness of ca. 4 m. Annual snow surveys and stream gauging reveal that the total input volume of snowmelt and rainfall to the meadow basin is several times larger than its groundwater storage capacity, giving rise to low total-dissolved species concentrations (14–21 mg/L) within the meadow groundwater. Observations from four piezometers established on the meadow show that the water table fluctuates rapidly in response to spring snowmelt and precipitation events but otherwise maintains a relatively stable depth of 0.3–0.4 m below the meadow surface during summer months. A slug test performed on one of the piezometers indicated that the saturated hydraulic conductivity of the shallow meadow sediments is 2.5×10−7 m/s. We suggest that a bedrock saddle imaged underneath the southern end of the meadow forms a natural constriction to subsurface flow out of the basin and helps to maintain the stable water-table depth.

认识美国加利福尼亚州谢拉内华达和阶梯山脉中受影响沼泽化草甸水文生态的一种框架

Meadows of the Sierra Nevada and Cascade mountains of California, USA, support diverse and highly productive wet-meadow vegetation dominated by sedges, rushes, grasses, and other herbaceous species. These groundwater–dependent ecosystems rely on the persistence of a shallow water table throughout the dry summer. Case studies of Bear Creek, Last Chance, and Tuolumne meadow ecosystems are used to create a conceptual framework describing groundwater–ecosystem connections in this environment. The water requirements for wet-meadow vegetation at each site are represented as a water-table-depth hydrograph; however, these hydrographs were found to vary among sites. Causes of this variation include (1) differences in soil texture, which govern capillary effects and availability of vadose water and (2) elevation-controlled differences in climate that affect the phenology of the vegetation. The field observations show that spatial variation of water-table depth exerts strong control on vegetation composition and spatial patterning. Groundwater-flow modeling demonstrates that lower hydraulic-conductivity meadow sediments, higher groundwater-inflow rates, and a higher ratio of lateral to basal-groundwater inflow all encourage the persistence of a high water table and wet-meadow vegetation, particularly at the margin of the meadow, even in cases with moderate stream incision.

Riparian hydroecology: A coupled model of the observed interactions between groundwater flow and meadow vegetation patterning

Stream incision is altering the hydroecology of riparian areas worldwide. In the Last Chance watershed in the northern Sierra Nevada, California, logging, overgrazing, and road/railroad construction have caused stream incision, which resulted in drainage of riparian meadow sediments and a succession from native wet meadow vegetation to sagebrush and dryland grasses. Restoration efforts have been initiated to reestablish the ecosystem function of these systems. Original field data including stream stage records, water table hydrographs, sediment hydraulic properties, topographic transects, and aerial imagery of vegetation patterning were used to develop a model of an archetype meadow. Hydrologic behavior was simulated with a finite element model of variably saturated groundwater flow. This model was coupled to an empirical, time‐dependent, vegetation threshold relationship between vegetation type and depth to the water table. This was a two‐way coupling requiring an iterative approach because water table depth is a determinant of vegetation type, yet the vegetation regime influences water table depth through evapotranspiration. The hydrology and vegetation patterns were analyzed under pristine, degraded (incised), and restored conditions. For the case of deep streambed incision, our hydroecological model predicts the observed shift from mesic (wetter) to xeric (drier) vegetation communities and reproduces their imaged longitudinal zonation. This patterning is explained as a response to groundwater drainage to the stream, which creates dry zones with xeric vegetation adjacent to the stream, while preserving sufficient moisture at the margins of the meadow to support holdout populations of mesic vegetation. The model further predicts the reestablishment of meadow vegetation when the incised channel is filled and a new shallow channel is restored. The coupling of a near‐surface hydrologic model to a vegetation response model may be used to design stream restoration projects by predicting vegetation patterning.

Sediment accumulation in a shallow-water meadow carpeted by a small erect bryozoan

Abstract A marine meadow covered 80–90% by a turf of the erect bryozoan Cellaria occurs over an area >104 m2 west of Banjole Island (Croatia) in the northeastern Adriatic Sea. Surrounding areas are bare to patchily covered by isolated clumps of bryozoans, sponges, and ascidians attached to scattered shell and rock debris. Silt and clay comprise >90% of the mass of sediment within the meadow, and Cellaria branch fragments are the next-most-abundant component. From 13-cm to at least 25-cm depth in the meadow sediment coralline algal branch fragments are abundant, and silt and clay comprise over 50% of the sediment's mass. In contrast, sediment accumulated in the bare area adjacent to the meadow is predominantly coarse carbonate sand composed of diverse skeletal grains. Mud comprises Concentration of mud in the sediment below the meadow apparently is due primarily to baffling by the erect bryozoans and earlier by the coralline algae, because composition and texture of the muds and fine sand are identical within and outside the meadow. The proportion of bryozoan skeletal fragments to mud in the upper sediment is similar to that of erect delicate bryozoans to sediment in shallow ramp buildups of Late Ordovician age in the southern Appalachians and of fenestrate bryozoans to mud plus cement in bryozoan-rich cores of Carboniferous mounds. The Paleozoic mounds also are surrounded by coarser sediment. By analogy with the Cellaria meadow, trapping and deposition of muds by erect bryozoans can be inferred for many of these Paleozoic mounds, even though bryozoans are a relatively small proportion of the total sediment.

Palynological evidence for 19th century grazing-induced vegetation change in the southern Sierra Nevada, California, U.S.A.

Summary Aim Stratigraphic pollen records are used to assess historic vegetation changes that have transpired in a North American mountain meadow since the introduction of Old World livestock species in the middle 1800s. Location Monache Meadows is located on the Kern Plateau in the Sierra Nevada mountain range, California, U.S.A. It is situated along the upper reaches of the South Fork Kern River in the southernmost drainage basin of the Sierra Nevada. Methods Short core samples of meadow sediments were extracted from five locations throughout Monache Meadows. These five samples are classified according to topographic position within the meadow – two upper meadow sites and three lower meadow sites. Stratigraphic analyses of fossil pollen from each core were used to assess vegetation composition before the introduction of European livestock (pre1850) and throughout the historic period (1850–present). The historic period geochronology is based on 210Pb dating of selected strata from each core. ResultsRiccia was a dominant taxon in the upper meadow before the introduction of grazing; Salix seems to have been more abundant in the lower meadow. Both Riccia and Salix decreased dramatically by c.1900, coeval with marked increases in Artemisia (upper meadow) and Cyperaceae (upper and lower meadows). Main conclusions Changes in meadow vegetation occurring during the latter part of the 19th century at Monache Meadows are attributed primarily to the introduction of European livestock (sheep and cattle). Other factors that may have contributed to the observed shifts in composition and dominance include changes in native herbivore populations and decreased fire frequency as a result of 20th century fire suppression policies.

Techniques for the concentration of foraminifera from coastal salt meadow sediments

Abstract. INTRODUCTIONConcentration of modern foraminifera from sediment samples is commonly performed by the heavy liquid carbon tetrachloride (CCI4) flotation method. From mainly inorganic, siliclastic sediments from marine habitats, about 94% of the foraminifera contained within a sample can be isolated in the first step (Lutze, 1968). This procedure is used in order to reduce the time taken to examine the foraminiferal content of a sample. However, it is not practical in all cases. Surface sediments of salt meadows from the west coast of the German Bight (southern North Sea) can be divided into two main types: (1) in seaward parts with only a patchy distribution of spermatophytes there is soft mud with a high content of detritus (faecal pellets and plant material) and low content of inorganic components (clay and finest sand); (2) in landward parts there is low moisture soil with a high content of living and dead plant roots similar to that of terrestrial meadows. Foraminifera of sediments of these kinds cannot be isolated by the flotation method for the following reasons.For sediment of type 1, if fractions 60–1000 μm (all clay eliminated by washing) have been dried in order to submit them to the flotation method, a serious problem arises. Flocky/grainy detritus aggregates to a cement-hard mass which encloses all the foraminifera. This ‘cake’ cannot be disaggregated without damaging or destroying the foraminifera.For sediment of type 2, when sediment treated the same way as sediment of type 1 is dried, fine plant remains, mainly . . .

The paleoecology and stratigraphy of Nichols Meadow, Sierra National Forest, California, USA

Sediment stratigraphy and pollen, plant macrofossil and charcoal analyses, along with nine radiocarbon dates from Nichols Meadow, provides the most intensive investigation of Sierra Nevada montane meadow development and paleoecology. During pollen zone NM-I (ca. 18,500-12,500 yr B.P.) the Nichols Meadow area contained a stream during the Tioga glacial stage. The presence of high Artemisia and Gramineae pollen percentages along with a very low pollen influx rate reflects a cold-dry steppe-woodland environment. Pollen zone NM-II (ca. 12,500-8800 yr B.P.) documents the development of a lower montane forest and giant sequoia ( Sequoiadendron giganteum) community which existed around a small meadow. The higher sediment accumulation rates suggest that fallen trees contributed to the aggregation of meadow sediments. arly Holocene aridity is recorded in pollen zone NM-III (ca. 8800-6000 yr B.P.) by poorly preserved pollen. We infer that the forest trees closed in on the meadow and occupied the meadow floor. The reduction in available moisture caused giant sequoia to become locally extinct in the Nichols Meadow area probably moving into their current distribution within the Nelder Grove. Pollen zone NM-IV (6000 yr B.P.-present) reflects the development of the modern Nichols Meadow. Less sand in the meadow sediments, due to stable vegetation surrounding Nichols Meadow, allowed the increased retention of ground water. This along with the neoglacial cooling trend at ca. 3000 yr B.P. caused ground water to rise and saturate the meadow. These events excluded the conifers from the meadow surface and allowed herbaceous vegetation associated with wet meadows to dominate. Overgrazing and channeling of the meadow's outflowing stream caused the water table to drop, resulting in the incision of the meadow.

Holocene floodplain evolution of small rivers in the uplands of Lower Saxony, Germany

The Holocene floodplain evolution of the river Ilme and its distal tributaries in the uplands of Lower Saxony (Germany) has been reconstructed by shallow corings arranged in cross and longitudinal profiles. In those river reaches that drain agricultural land we differentiate three Holocene fluvial units overlying the Weichselian Lower Terrace: A fine-grained Humus Basal Layer (early-middle Holocene), an Older Meadow Loam (8th-early 14th century) and a Younger Meadow Loam (since 15th century). Intertongued with these sediments are alluvial fans and colluvia of two periods: 1. Neolithic to early Medieval time, 2. 14th century. In contrast forested floodplains are underlain by sand and gravel, whereas on floodplains used as meadows, a fine-grained “Wiesensediment” (Meadow Sediment) has accumulated since the 17th century. The Humus Basal Layer and the sandy gravel were both accumulated by braided rivers. In the middle and lower reaches of the Ilme floodplain, the change to a meandering river happened when the Older Meadow Loam accumulated as a result of woodland clearing and soil erosion in the Early Middle Ages. In the course of time, the vertical accretion of the floodplain decreased as a result of the decreasing frequency of inundations, itself caused by the increasing capacity of the river channel. Vertical accretion was nearly terminated in the Late Middle Ages when a short climatic change caused fan and colluvial deposition. Since the 15th century, the Younger Meadow Loam accumulated, most of it filling old channels. In the wooded Solling hills, the change-over from a braided river to a meandering river began in the 17th century, but in those reaches with wooded floodplains the rivers are still braided.

Modern pollen rain within and adjacent to two giant sequoia (Sequoiadendrongiganteum) groves, Yosemite and Sequoia national parks, California

Analysis of modern pollen (from polsters) and plant percentage coverage (from relevés) within and near two giant sequoia (Sequoiadendrongiganteum) groves provide data on the relationship between plant abundance and pollen dispersion. Most Sequoiadendron pollen is deposited within or near the groves, substantiating previously established theoretical models on pollen dispersion. Within the groves, Sequoiadendron is only slightly overrepresented by its pollen (R value average, 1.6). At the Tuolumne Grove, Sequoiadendron pollen averages 1.5% at stations within 450 m of the grove boundary. Pollen percentage is slightly higher (8%) for similar stations at Lost Grove. This contrasts with the more widely dispersed pollen of Pinus and Quercus, and the less widely dispersed Chrysolepis and Cornus. Patterns of pollen dispersal away from the groves are consistent with the prevailing wind direction and diurnal air mass movements. For Sequoiadendron, the relatively poor dispersal has implications for future paleoecologic studies interpreting the sedimentary pollen record from meadow sediment cores; and for understanding the exchange of genetic information between these trees that grow in stands somewhat isolated from each other.