Total Suspended Solids

How have total suspended solids (TSS) in the Great Bay Estuary changed over time?

Suspended solids at Adams Point show a statistically significant trend since 1989. At the Great Bay Station, there is no statistically significant trend in the data going back to 2002.


Total suspended solids (TSS) are what is left over when a water sample is filtered and dried. While a small percentage of phytoplankton or pieces of plant matter remain, most of TSS is made up of sediment. Suspended solids come from resuspension within the estuary as well as erosion from streambanks, salt marshes and the upland portion of the watershed. This material is then delivered to the estuary via tributaries. Increasing suspended sediments reduce water clarity, and impact primary producers such as eelgrass, seaweeds, and phytoplankton.
No increasing trends for total suspended solids.
Total suspended solids have increased at Adams Point since 1989 (Figure 2.1). The average median value for the first 13 years of the dataset (1989-2002) was 12.0 mg/L. For the second half of the data set (2003-2015), the average median value increased to 22.9 mg/L, an increase of 90%. In contrast, suspended solids have remained relatively stable at the Great Bay station since 2002. In 2015, the median concentration was 14.1 mg/L (Figure 2.2).

More research is necessary to understand the source and transport of sediments in the Great Bay Estuary. For example, decreases in eelgrass and oyster habitats lead to greater resuspension of sediments, but sediments may also be added to the estuary from the tributaries or the estuary shores.

Higher suspended solids concentrations have the potential to harm eelgrass and oysters. Anything that reduces light to eelgrass leaves can add stress. In addition, sediment build-up on leaves can inhibit gas exchange. Oyster monitoring efforts show that oyster reefs that do not build high enough above the estuary floor can be smothered by sediment deposits.

It is important to acknowledge however, that a certain amount of sediment supply is necessary to maintain salt marsh elevations and sediment supply is a key factor in determining salt marsh resilience to rising sea levels and potential migration.

Figure 2.1 Total suspended solids at Adams Point Station. Box and whisker chart of data collected at low tide only. The horizontal line in each box is the median. Boxes encompass the middle 50% of the data points. Upper and lower vertical lines show the complete range of data values. Year 2001 not included due to missing data.

Figure 2.2 Total suspended solids at Great Bay Station. Box and whisker chart of data collected at low tide only. The horizontal line in each box is the median. Boxes encompass the middle 50% of the data points. Upper and lower vertical lines show the complete range of data values.