The short version
Water in northeastern US estuaries has warmed by roughly a degree Celsius since the 1960s. Scientists at the US Environmental Protection Agency’s lab in Narragansett, Rhode Island, asked whether the very shallow edges of estuaries, less than about 3 feet (1 m) deep, might be warming even faster. By piecing together old records from two Rhode Island estuaries, they found hints that these shallows may be warming about three times faster than deeper water. The authors stress that the evidence is preliminary.
What the researchers did
Long-term temperature monitoring usually happens offshore, in deeper water, so few long records exist for the shallow shoreline. The team set out to repeat a 1962 fish survey and, along the way, took a close look at water temperatures at the same four spots.
- They sampled four shallow stations in the Narrow River and Point Judith Pond in southern Rhode Island in 2010–2012, matching the locations of a 1962 master’s thesis study.
- They compared their temperatures with older year-long records from the same sites (1967–68 for Point Judith Pond and 1972–73 for the Narrow River), gathered from theses, reports and other “gray literature.”
- They also compared their readings with nearby deeper-water stations and with NOAA’s long-term record at Newport, and repeated the 1962 beach-seine fish counts.
What they found
- Much more warming in the shallows. Average annual temperatures at the four shallow stations were 3.3–4.7 °C higher than in the earliest records, an average of 3.9 °C (about 7 °F). Leaving out the unusually warm year of 2012, the average was 3.5 °C. For comparison, the paper cites about 1.4 °C of warming in northeastern estuaries such as Woods Hole and Narragansett Bay since the 1960s.
- Winter and spring warmed most. Summer and fall temperatures were not significantly different from 1962. As in Woods Hole and Narragansett Bay, the biggest changes showed up in winter and early spring.
- Depth helps explain it. Shallow water holds less heat, so it warms quickly. The authors’ rough calculation shows that the same sunshine could warm 1 m of water by about 2 °C in a day, compared with about 0.2 °C for a well-mixed 10 m column.
- More, bigger fish. Fish catches in 2010–2012 were 4 to 8 times higher than in 1962. Silversides (Menidia) made up 78–87% of the catch, up from 35–52%, and were on average 70% larger in summer.
- Big caveats. The records came from many studies using different methods. The authors say the uncertainty is high and call for a regional effort to find similar data elsewhere in southern New England.
What it means for Waquoit Bay today
Waquoit Bay is a shallow estuary, much like the Rhode Island salt ponds in this study, and much of it is only a few feet deep. If shallow water really warms faster, our bay’s edges and coves may be warming more than regional averages suggest. The authors note that nitrogen pollution drives eelgrass decline and that warmer water makes that effect worse. They conclude that shallow waters may be important places to look for the effects of climate change
(Oczkowski et al., 2015).
We can’t control water temperature locally, but we can control nitrogen. Warming is one more reason the nitrogen limits in the towns’ wastewater plans matter: a warmer bay will likely have less room for error. The study also points to the value of long-term, nearshore monitoring like that done by the Waquoit Bay National Estuarine Research Reserve.
Read the paper
Oczkowski, A., McKinney, R., Ayvazian, S., Hanson, A., Wigand, C., & Markham, E. (2015). Preliminary Evidence for the Amplification of Global Warming in Shallow, Intertidal Estuarine Waters. PLOS ONE, 10(10), e0141529. https://doi.org/10.1371/journal.pone.0141529
License: This article is free of all copyright and is released under the Creative Commons CC0 public domain dedication. The full PDF below is reproduced unmodified from the publisher, PLOS. The research was funded by the US Environmental Protection Agency but was not subject to Agency review. The card image is Figure 1 from the paper (CC0).
Drafted with AI assistance from the linked source.
