Plant Colonisation, Soil Development Processes and Characterization of Quarried Land in Ndarugu, Kiambu County

Abstract

In Kenya, demand for building materials has continued to increase due to growth in the real estate industry and rapid urbanisation in general. Ndarugu region in Juja, Kiambu County, is one of the zones where stone quarrying has intensified. The objectives of this study were; (i) to assess the management status, Cultural characteristics of post-quarry sites, and perception of stone quarry land owners on impacts of stone quarrying, (ii) to determine the type of plant composition and microsite organization of land surface materials, (iii) to assess level of post-quarry site substrate development and (iv) to determine soil macrofauna composition for land surfaces disturbed by stone quarrying. The assessment was done for quarry sites under different management regimes and at different periods of post-quarry activity as determined from a survey of quarry site landowners. Survey for landowner’s perception and quarried land characterization was undertaken using a questionnaire survey instrument on systematically sampled homesteads. From the questionnaire survey, a total of 60 quarried sites were identified. Nine sites aged between 1 and 20 years were selected through the use of inclusion criteria and were used in assessing plant composition, microsite organisation of land surface materials (patch type, width, length, number; and inter-patch type and length), and soil development in both the wet and dry seasons, following the landscape functional analysis (LFA) method. Soil macrofauna composition was investigated by sampling five 25 cm by 25 cm quadrats per site, in which macrofauna was identified to family and species level and numbers recorded. All the data collected were analysed using a statistical package for social science (SPSS) v.25. Descriptive and inferential analysis (Kruskal Wallis test, Mann Whitney u test) were undertaken. From questionnaire survey, the oldest stone quarry was in 1989 although in majority of the quarry sites quarrying was ongoing. Creation of employment opportunities and opening up of the interior areas were perceived as the main positive impact of quarrying, while the influx of new people and dust pollution were perceived as the main negative impact of quarrying. Backfilling with local soil was the main method used to rehabilitate the quarried land, although most of the quarried sites were naturally rehabilitating. Lack of financial support and lack of a compulsive legal framework were perceived as main limitations to land rehabilitation. From the assessment of the microsite organisation, one inter-patch type, bare soil (BS); and four resource accumulation surface types (patch); plant stone complex (PSC), plant complex (PC), single plant (SP) and stone complex (SC) were identified. Patch and inter-patch densities were found to be high among the young quarries (1-5 years) and lowest in the old quarries (16-20 years). The difference in patch density was statistically significant between the age categories. Patch width and landscape organisation index was high during wet season and in older quarry sites and the difference only significant across age category. was not significant (p<0.05). For transect plant composition, a total of 178 plant species belonging to 41 plant families were identified; 163 and 173 plant species in dry and wet seasons respectively. The 16-20 years’ category had the highest mean species number per 10 m along the transect while 1-5years category had the least both in the dry and wet season. Backfilled with local soil and not levelled rehabilitation category recorded the highest number of plant species. In soil development, infiltration, stability and nutrient cycle indices were higher during the wet season as compared to dry season and the difference was statistically significant (p<0.05). The soil indices were found to increase with increase in the quarry age. The rehabilitation methods used in quarried sites were found to significantly influence soil development. For macrofauna composition, a total of 100 quadrats were surveyed during the wet and dry season in the 9 quarry sites. A total of 72 species of macrofauna were identified belonging to 15 fauna orders. The order Coleoptera was the most common order represented by 25 species of macrofauna. The wet season was found to have higher macrofauna diversity as compared to the dry season. Mean fauna species richness per quadrat was found to increase with increase in quarried land age. Backfilled with local soil not levelled rehabilitation method recorded the highest species richness while backfilled levelled planted with trees saplings recorded the highest diversity index. The study identified existence of the impact of quarrying activities on the landowners and surrounding communities in the quarry zone. The study identified plants species that can grow in the stone quarried sites which provides basis for plants that can be used to rehabilitate quarried sites. Age and rehabilitation methods were found to influence soil development, macrofauna diversity and plant composition.