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Forest clear cutting alters the hydrological processes such as interception, evapotranspiration and infiltration of the forested watershed and consequently increases the amount of water and sediment leaving the watershed. This study was conducted in the Upper Pearl River Watershed (UPRW) located in east-central Mississippito evaluate and compare the potential impacts of forest clear cutting on water and sediment yields using the Soil and Water Assessment Tool (SWAT) model. For this purpose, five hypothetical scenarios representing clear cutting at 10%, 20%, 30%, 55% and 75% of the total forest area of the watershed were generated. The SWAT model was first calibrated (1981-1995) and validated (1996-2008) for monthly stream flow, and later verified (February 2010 to December 2010) for monthly sediment load. Results show that the SWAT model was able to simulate stream flow and sediment load satisfactorily during the calibration/validation and verification periods, respectively. The potential changes caused in yields as a result of the changes in clearcut area were computed by comparing predicted yields from each clear cutting scenario and a base condition. Results from five scenarios demonstrate substantial increase in yields with an increase in the percentage of forest area clearcut. When compared with the base scenario, potential changes in water and sediment yields occur between 17% to 96% and 33% to 250%, respectively, with an increase in clearcut area from 10% to 75%. Results also indicate that, for all scenarios, percentage wise change is larger for sediment yield. Although predicted water and sediment yields generated from each scenario are subject to further verification with observed data, this study provides useful information about the potential amount of water and sediment yields that may be produced under each scenario, and that the potential changes that may happen on yields if similar magnitude of clear cutting occurs in the UPRW or in similar watershed.
Independent observation of the effects
of agricultural management practices on soil organic carbon (SOC) with soil moisture
content (SMC) is essential to quantify their potential relationships for
sustainable ecosystems. Soil water retention studies and soil carbon stocks
have been mapped in some areas worldwide. However, few studies have been conducted
in the southeastern US, particularly in Mississippi.
The objectives of this research study were to collect soil samples from fields
chosen to be representative of the watersheds they are contained within,
analyze the soil samples for carbon content and soil moisture content, and
evaluate the relationship between SOC and different parameters (land use,
vertical distribution, temporal distribution, and soil moisture content). Field
sites were chosen based on their compositional similarity shared with the
watershed as a whole in the Town Creek watershed (TCW) and Upper Pearl River
watershed (UPRW) in Mississippi.
Monthly soil samples from different depths (6 inch, 12 inch, and 24 inch) were
collected from crop, pasture, and forest field areas. Soil samples were
analyzed using bench analysis, elemental analysis, and statistical analysis.
This study was able to demonstrate the SOC distribution in the soil layers
across all three land uses studied. It was also shown that there does seem to
be an interactive effect of parameters such as land use type, vertical
distribution, and time on carbon accretion within the soil. Results of this
study also determined that the near surface (6-in) layer was found to contain
significantly more carbon than either the 12 inch or 24 inch layers (p < 0.01) across all field types. There
was found to be a high degree of variability within the soil moisture data and
correlation between SOC and SMC. It was found that carbon amount is not
influenced by SMC but SMC could be influenced by SOC.
analysis of crop parameters and the performance of SWAT (Soil and Water
Assessment Tool) model to simulate potential forest biomass production were
evaluated for the Upper Pearl River Watershed (UPRW). Local sensitivity
analysis of seven crop parameters: radiation use efficiency (kg/ha)/(MJ/m2)
(BIOE), potential maximum leaf area index for the plant (BLAI), fraction of
growing season at which senescence becomes the dominant growth process (DLAI),
fraction of the maximum plant leaf area index corresponding to the 1st point on
the optimal leaf area development curve (LAIMX1), fraction of growing season
corresponding to the 1st point on the optimal leaf area development curve
(FRGRW1), plants potential maximum canopy height (m) (CHTMX), and maximum
rooting depth for plant (mm) (RDMX) reveals that only three parameters: DLAI,
BIOE and BLAI are sensitive to forest biomass production. Further, results
indicate moderate sensitivity of DLAI and BIOE and low sensitivity of BLAI
with relative sensitivity index of 0.44, 0.35 and 0.14, respectively. The
performance of SWAT to simulate potential forest biomass was evaluated by
comparing simulated data against three years of observed data that were
obtained from USDA Forest Service website. The results indicate satisfactory
performance of SWAT in predicting potential forest biomass, which is shown by
the high value of coefficient of determination (R2 = 0.83), small
root mean square error (RMSE = 11.11 Mg/ha), and small difference between mean.
Results also reveal that the UPRW has the potential to produce approximately 49
Mg/ha of average forest biomass annually, which is approximately 6% less than
the observed biomass.