Assessing the impact of soil hydrocarbon properties on plant functional types using hyperspectral data in the Niger Delta

The presence of soil hydrocarbon parameters (SHPs), including total petroleum hydrocarbons
(TPHs), total organic carbon (TOC; %), and soil toxicity (EC50; mg L−1), can affect
vegetation in several ways. This study assessed the impact of SHPs on vegetation in the
Niger Delta using field-measured, leaf-scale hyperspectral data acquired across the region.
Red-edge position (REP) and four hyperspectral vegetation indices (HVIs)—mND705,
photochemical reflectance index (PRI), Normalised Difference Vegetation Vigour Index
(NDVVI844,447; a vegetation vigour index), and modified DATT (MDATT; a chlorophyllsensitive
red-edge index)—were used to quantify chlorophyll content in the vegetation
types of Awolowo grass, elephant grass, mango trees, oil palm trees, and mangrove vegetation
and to explore their variation with SHPs. The results show that mangrove vegetation
was the most impacted by TPHs (R = −0.683), while mango vegetation was the most
impacted by TOC (R = −0.725), based on Pearson correlation coefficients derived from the
mND705 index. Similarly, mango and mangrove vegetation showed the strongest responses
to soil toxicity (EC50; mg L−1), based on Spearman correlation coefficients (rs = 0.657 and
rs = 0.870, respectively) using the MDATT index. These findings highlight species-specific
physiological responses to soil hydrocarbon contamination and demonstrate the applicability
of red-edge-based hyperspectral techniques for assessing vegetation stress in complex
coastal ecosystems such as the Niger Delta.