The growth of the weeds near the mangrove forest can also bring in destructive herbivores such as locust, caterpillars and insect pests that feed on leaves. In the Niger Delta there are limited studies to address these questions. Therefore, this study is aimed at investigating the diversity of weed and other plant species found in sand filled mangrove forests, and to determine the concentration of some heavy metals in soil and plant. The objectives of this study are: 1) to determine the diversity index  and importance value  of the weed species 2) to determine the THC and heavy metal concentration in both soil and plant, and 3) to compare the THC and heavy metal concentration in plant and soil. The study area is an abandoned sand dump located at Eagle Island , directly behind the Rivers State University . The area has a warm and humid climate with two seasons, dry and wet seasons . The soil of the area is between sandy to muddy, and also whitish to dark brown in color . The area was once a mangrove forest, but was cut down to make way for sand mining five years ago. At the end of the sand mining activity the area was later abandoned to its fate. The company that operated the sand mine left the site with heaps of white sand still on the ground surface .

This abandoned sand became a plat form on which a variety of weed and other plant species grow over the years. These species are plants that naturally cannot grow in swampy soil but because of the conversion of the sand from swampy to sandy soil weeds do proliferate. Moreover, the site is surrounded by a river channel which brings in sediments and seeds of plants during high tide. At the edges of the sand dump are heaps of mangrove soils placed to prevent the entry of water during high tide. Heavy metal extraction followed the example of . Aliquots of 0.25 g of air dried sediment samples were weighed into a Teflon inset of a microwave digestion vessel and 2 ml concentrated  nitric acid  were added. The metals were extracted using a microwave accelerated reaction system  at 1500 W power , ramped to 175˚C in 5.5 min, held for 4.5 min,cannabis grow tent and allowed to cool down for 1 h. The cool digest solution was filtered through the Whatman 42 filter paper and made up to 100 ml in a volumetric flask by adding de-ionized water. All chemicals and reagents used were of analytical grade and of highest purity possible. Analytical blanks were prepared with each batch of the digestion set and analyzed  in the same way as the samples. The detection limit for the three metals analyzed in mg/l i.e. Zinc, Cadmium and Lead is 0.001, 0.001 and 0.002 respectively. Mangroves are habitat specific, and grow only in swampy soils.

This is because most mangrove species apart from A. aureum  cannot grow well in sandy soil because it has low salinity and conductivity . Mangrove swamp is one of the largest carbon sequesters in the world this is because of their air purification ability and high productive capability . Swampy soils have higher heavy metal load because of their exposure to oil spillages from oiling activities onshore and offshore. Pollution of the shorelines destroys swampy soils by reducing salinity and destroying microbes within the soil. A known characteristic of mangrove swamp is their ability to carry out decomposition , which has made them a biodiversity hot spot . But when human activities of deforestation, sand mining and urbanization degrade the soil it becomes difficult for them to carry out their function as host to numerous soil dwelling organisms. This enables opportunistic invasive species and weeds to come in to colonize the area . In this study, previous sand mining activity destroyed the swampy soil, and in its place sandy soil was deposited, which facilitated the proliferation of weeds .

The role played by weeds in this study area is not well known but need further studies. However, the result indicates that weeds present in the sand filled area absorbed the soil pollutants. This is shown by Figure 3, where weed concentration of THC and heavy metal was more than that of the soil. It shows that the weeds are acting as bioremediation agents. Mangrove swamp has hydrocarbon utilizing bacteria that degrade pollutant to a less harmful level The weed species from field observations are acting as host to pollinators such as butterflies, cricket, beetles and mosquitoes, to mangrove; this is a positive role by weeds . However, they can be detrimental to humans by hosting harmful insects and rodents. Field experiences had shown that most mosquitoes that reside in mangrove forest always go to roost on nearby weed and enter the mangroves to feed on animals, which is a negative role because of the proliferation of mangroves parasites in Africa .