###### Abstract  
The sediment pollution index acts as a useful indicator for assessing anthropogenic pollution within river drainage basins. An industrialized urban river, Fengshan River in Kaohsiung City, southern Taiwan has been suffering heavy metal pollution from surrounding factories. In this study, spatial and seasonal variations in heavy metals in sediments from seven sampling sites of Fengshan River were determined to assess sediment pollution status and potential ecological risk using multiple sediment pollution indices. Results showed that the heavy metal concentrations displayed large spatial variations. Severe contamination of heavy metals, especially for Cr, Hg, and Zn in the lower reaches of Fengshan River, may attribute to wastewater discharges from leather processing and metal finishing factories along the river drainage basin. An increase in metal concentrations from upstream to downstream indicated that heavy metals tend to accumulate in tidal reaches, probably as a result of the flocculation effect. Frequent heavy rainfall in the wet season can enhance surface runoff to discharge metal pollutants from non-point sources (scattered factories) into the river. Assessment of multiple pollution indices showed moderately polluted (mCd = 3.9, PLI = 2.6) and considerable ecological risk (RI = 540, mERMQ = 0.55), indicating Fengshan River sediments, particularly in the lower reaches, are considered toxic and can cause adverse effects to benthic organisms. Organic matters showed a good correlation with heavy metals, which play an important role in the spatiotemporal variations in heavy metal pollutants in the Fengshan River sediments. This study can provide valuable information for river pollution remediation, and urban planning and management. heavy metal; river sediment; pollution index; ecological risk +
Footnote †: journal: Applied
conditions) [5]. Moreover, heavy metal pollutants are not fixed permanently in the sediments, which may be desorbed/dissolved and released into the water column through the immobilization processes, negatively affecting water quality [6]. Thus, sediments act both as sinks and sources for heavy metals and strongly affect their distribution in river environments, playing an essential role in determining the pollution pattern of river systems [7,8]. Therefore, river sediments are valuable indicators for assessing anthropogenic pollution within river watersheds. However, direct determination of heavy metal concentrations in sediments may not be suitable to assess the heavy metal pollution status and potential risks to exposed aquatic organisms; as heavy metals may be of natural or anthropogenic origin [9,10]. Therefore, the assessment of the sediment pollution level depends on sediment quality guidelines (SQGs) derived from numerous data of biological responses from aquatic organisms, including threshold-effects-level (TEL), probable-effects-level (PEL), effects-range-low (ERL), and effects-range-median (ERM) guidelines [11,12]. The SQGs can provide quick information on identifying the sediment quality and probability of biological toxicity. Based on the SQGs, many derived ecological and chemical approaches, such as mean ERM quotient (mERM\({}_{\text{Q}}\)) and the contamination severity index (CSI), have been used to evaluate the ecological risk of toxic metals for aquatic lives and the potential adverse effects on infaunal animals [13,14]. Furthermore, several contamination indices such as contamination factor (CF), geo-accumulation index (I\({}_{\text{geo}}\)), and pollution load index (PLI) have also been widely used to distinguish anthropogenic pollutants from the natural background [15,16]. Therefore, whether it is a large natural river or a small river in an urban area, the heavy metal pollution level can be assessed using the sediment quality guidelines and the sediment pollution indices.