Tunje Mwamuye Pole^1,, Mwakio Tole¹, Suhaila Hashim²

Quarrying activities create significant health, environmental and visual impacts which require to be addressed through the implementation of some rehabilitation practices. The process usually starts and proceeds using key steps following a decision to reach a targeted desired final ecosystem. As the processes progresses however, the most important factor considered to affect ecosystem integrity, is soil quality which is determined using the physicochemical and biological characteristics for ecosystem structure and function. Literature has indicated that most past ecosystem rehabilitation research has been using inaccurate, time consuming and costly methods. This study evaluated the changes among selected soil physicochemical properties and enzyme activity as measures of the quarry rehabilitation status. The study analyzed the soil bulk density (BD), organic matter (OM), pH, nitrates (NO₃^-_-N), nitrites (NO₂^--N), ammonium ion (NH₄⁺), phosphates (PO₄^3-) and Cation Exchange Capacity (CEC) of the Tezo rehabilitated quarry sites in Kilifi County, Kenya. In addition, amylase, cellulase and protease enzyme activities were also evaluated. Soil samples were collected from early (< 10 years), intermediate (11 – 20 years) and mature (> 20 years) rehabilitation plots. Undisturbed virgin plots and abandoned plots which were recovering naturally represented the control plots. Findings showed that soil bulk density was significantly different (P ˂ .0001) and was highest among the intermediate and early plots while the mature plots had the lowest BD values. Relative to soil organic matter, the study results showed that BD decreased as OM increased among all the plots. Additionally, soil OM revealed significant difference (P ˂ .0001) among all plots while reporting a general increase with rehabilitation stages. All the selected soil chemical parameters revealed significant differences (P ˂ .0001) across all rehabilitation stages. Both nitrates and nitrites ions were highest within intermediate plot but on the contrast, nitrates were lowest within early plots while nitrites were lowest within the virgin plots. The highest ammonium ion levels were reported in mature plot which were twice that of the early plots while phosphate levels were however, highest among the natural sites but similarly lowest within the early plots. Virgin plots reported CEC levels that were about 2.5 times higher than the early sites. Soil pH measurements were within a narrow range of between 7.7 and 8.6 between the lowest and highest value. Except protease enzyme activity, which had significant differences (P ˂ .02) only among the naturally recovering plots, amylase and cellulase were significantly different across all plots at different rehabilitation stages. There were, in addition, strongly to moderately positive correlations between amylase and cellulase with organic matter, nitrates, nitrites ammonium and phosphate ions. Protease activity however, revealed negative correlations with organic matter. The study therefore identified, due to their consistent trend, OM, CEC, ammonium phosphate ions as well as amylase and cellulase activity as being the most reliable soil quality indicators that can be used to predict the rehabilitations status of quarries.

Rehabilitation, physicochemical properties, ecosystem integrity, enzyme activity