Mikrohabitat dalam struktur tanah
Di setiap tempat seperti dalam tanah, udara maupun air selalu dijumpai
mikroba. Umumnya jumlah mikroba dalam tanah lebih banyak daripada dalam air
ataupun udara. Umumnya bahan organik dan senyawa anorganik lebih tinggi dalam
tanah sehingga cocok untuk pertumbuhan mikroba heterotrof maupun autotrof.
Keberadaan mikroba di dalam tanah terutama dipengaruhi oleh sifat kimia
dan fisika tanah. Komponen penyusun tanah yang terdiri atas pasir, debu, lempung dan
bahan organik maupun bahan penyemen lain akan membentuk struktur tanah. Struktur
tanah akan menentukan keberadaan oksigen dan lengas dalam tanah. Dalam hal ini
akan terbentuk lingkungan mikro dalam suatu struktur tanah. Mikroba akan membentuk
mikrokoloni dalam struktur tanah tersebut, dengan tempat pertumbuhan yang sesuai
dengan sifat mikroba dan lingkungan yang diperlukan. Dalam suatu struktur tanah
dapat dijumpai berbagai mikrokoloni seperti mikroba heterotrof pengguna bahan
organik maupun bakteri autotrof,dan bakteri aerob maupun anaerob. Untuk
kehidupannya, setiap jenis mikroba mempunyai kemampuan untuk merubah satu
senyawa menjadi senyawa lain dalam rangka mendapatkan energi dan nutrien. Dengan
demikian adanya mikroba dalam tanah menyebabkan terjadinya daur unsur-unsur
seperti karbon, nitrogen, fosfor dan unsur lain di alam.

Non-Statistical Approaches....

Non-Statistical Approaches for Comparing Site and Background Data]

For most sites, a determination of whether site concentrations represent
background conditions can be made without using statistical tests. The basic approach is to define the upper end of the range of background concentrations as the lower of:
1) The maximum background concentration, or
2) Twice the mean background concentration.
The maximum concentration on site is compared with this upper limit on
background. If the maximum concentration found on site is less than or equal to this upper background limit, the chemical can be considered to be background and removed from further consideration in any risk assessment or site remediation decisions.
This approach has been used for decades and has widespread regulatory
acceptance. It is simple, conservative, and works with a limited number of background samples. When conducting this test, the following points apply:
• A minimum of seven background samples is needed (i.e., data from seven
different background locations).
• Both background and site samples should be discrete rather than composite
samples. Discrete samples are needed to identify the maximum background and
site concentrations, which are critical for this test.
• As noted above, comparisons should be made with equivalent soil horizons. In
general, data from different soil horizons should not be combined unless the
absence of concentration change with depth can be clearly demonstrated.
• For “non-detect” background samples, one-half the detection limit should be used in calculating the mean background concentration.
If site concentrations are above background, and background concentrations are
above risk-based criteria, cleanup to background levels may be warranted. In this
situation, the site-specific upper limit on background (i.e., the lower of the maximum or twice the mean background concentration) can be used as a not-to-exceed cleanup criterion. That is, removal or management of all concentrations above this value will be considered to have restored the site to background conditions with respect to this contaminant.
Another non-statistical approach involves a comparison of the 95% UCL of site
samples with the 95% UCL for background. This method has technical limitations that could, in theory, lead to misclassification of contaminants as background, or not background. The approach is accepted, however, while the Department evaluates its performance in practice. Consistent with requirements for using a 95% UCL in Chapter 62-780, F.A.C., a minimum of 10 samples is needed, of which seven must be above detection limits (or three above detection limits to use the Bounding Method). This minimum sample requirement applies for both site and background samples at each soil horizon. Also consistent with Chapter 62-780, F.A.C., the maximum concentration on the site should be less than, or equal to, 3-times the default CTL. The 95% UCL approach should not be used for chemicals with CTLs based on acute toxicity when exposure scenarios with children are plausible (e.g., residential land use, parks, schools).

Where to Obtain Background Concentration Information

Where to Obtain Background Concentration Information
Background concentration information is derived on a site-specific basis using
samples from nearby “background” locations. The basic principle in identifying
background sampling locations is to find areas that resemble as closely as possible soil conditions at the site had a discharge or release not occurred. The selection of background sampling locations is a matter of professional judgment, but the following points should be considered:
• The background sampling area must be clearly unaffected by releases from the
subject site, or any other site. When characterizing natural background conditions,
samples are best taken from areas with minimal anthropogenic impact (e.g., natural areas and parks). In e stablishing anthropogenic background, sampling in areas where contaminants may accumulate should be avoided unless data are needed specifically for comparison with similar features found on a site. These data should be evaluated separately from other anthropogenic background samples. Because selection of background sampling locations is a matter of professional judgment, it is best to obtain concurrence from FDEP staff before obtaining background samples. The following areas are inappropriate to sample when determining soil background:
1. Fill areas;
2. Areas where known or suspected hazardous substances, petroleum, solid or
hazardous wastes or waste waters are managed, treated, handled, stored or
disposed;
3. Areas affected by runoff from a roadway;
4. Parking lots and areas affected by runoff from parking lots or other paved areas;
5. Railroad tracts or railway areas or other areas affected by their runoff;
6. Areas of concentrated air pollutant depositions or areas affected by their runoff;
7. Storm drains or ditches presently or historically receiving industrial or urban
runoff
• Natural concentrations of inorganics can vary with soil type. When determining
natural background, the soil type for the site and background locations should be
the same, if possible.
• Both natural and anthropogenic chemical concentrations can vary with soil depth. Consequently, background samples should be taken from the same soil horizon(s) as the site soil samples.
• Concentrations from background studies published in the literature cannot be used as the basis of comparison with site concentrations. Published background studies may be of value in determining whether a site-specific background data set lies within the range of observations by others. If not, the validity of the site-specific background data set may need to be evaluated.
• In measuring chemical concentrations in background samples, the same analytical methods used for site samples should be employed.
• The background data set should be examined carefully for the presence of
outliers, i.e., data that may not in fact represent background conditions. Formal
outlier tests as well as professional judgment can be used in evaluating the
background data set.

Concentrations

Concentrations
Land is a natural resource that is essential for the existence of life and is the variable
factors for which management has become most essential.
Land provides food, fuel, fodder and shelter besides supporting secondary and other
economic life supporting system. However there has been a continuous depletion of land
resources and the quality of land is deteriorating due to various factors like soil erosion
caused mainly due to shifting cultivation, large scale deforestation, reckless mining
activities, overgrazing, general mismanagement etc. Such soil erosion lead to degradation
of soils’ physical property and loss of plant nutrients.
It takes nature 600-1000 years to build 2.5 cm of top soil but get displaced in a year due to misuse, as a result it become the harmful single factor in the deterioration of productive land. It has been proved that soil lost from unprotected land is about 120 tons ha-1 yr-1 and may go as high as 300 tons ha-1 yr-1.
Thus, a part from depletion of fertile soil erosion results in the loss of run-off water, plant
nutrients and micro flora, siltation of reservoirs and riverbeds thereby adversely affecting
irrigation and power potential; causing floods in plain and valley which damage crops,
animals, habitation, communication etc. But most of all it adversely affect agricultural
production, forest production and availability of water both for irrigation and drinking
besides bringing about a disturbance in the soil and water balance. So, Objective of Soil Conservation
· Enhancing and sustaining productivity of available land stock for primary production
systems of crop cultivation livestock raising and forest management.
· Generating additional employment opportunities and income through secured
livelihood in rural areas.
· Maintaining beneficial relationship between land and water cycles and deter /
moderate hazards of droughts and flood.
· Retarding Watershed degradation caused by deforestation, soil erosion,
sedimentation, land degradation and hydrologic deterioration of the watersheds.
· Locating, reclaiming and developing cultivable wastelands, fallows other than current
fallows and degraded lands to meet increasing and competing demands for additional land stock for various sectors.