A landscape contractor purchased 10 dump-truck loads of "topsoil" excavated from a black, rich appearing soil in a coastal wetland. Samples of the soil were in immediately sent to a lab to be sure they met the specified properties (silt loam texture, pH 6 to 6.5) for the topsoil to be used in a landscaping job. The lab reported that the texture and pH were in the specified range. so the topsoil was installed and an expensive landscape of beautiful plants established. Unfortunately, within a few months all the plants began to die. Replacement plants also died. The topsoil was again tested. It was still a silt loam. but now its pH was 3.5. Explain why this pH change likely occurred and suggest appropriate management solutions.