By the end of the 19th century, naturalists had been probing the Chesapeake Bay for nearly two centuries, from Anglican Hugh Jones, through Thomas Jefferson on to the dilettante specialists in everything from fossils to diatoms and jellyfish.
Interest in the Bay’s biology increased after the Civil War, as the Bay began producing phenomenal fishery yields.
The available information did little to explain how the Bay could be so productive nor did it help in the understanding of what the food sources and environmental conditions were which both attracted and sustained these valuable populations. The concept of ecology — understanding the system as a functional whole — was not yet current and the process of understanding was tackled piecemeal.
P.R. Uhler and Otto Lugger published a list of Maryland fishes in 1876. While their list and descriptions lack illustrations, they commended readers to:
“...the large collection of specimens now on exhibition in the Museum of the Maryland Academy of Sciences, and there they are daily open to the inspection of the public, free of charge for admission.”
They realized, though that the Bay was changing and commented on the then-recent disappearance of anadromous shad and herring runs from several Upper Bay rivers, especially those around Baltimore.
These early “management questions” were investigated by the U.S. Bureau of Fisheries, which had been founded by Spencer Fullerton Baird in 1871.
Most of the Chesapeake surveys, begun in 1915, were conducted aboard the U.S.S. Fish Hawk although there are also references to the U.S.S. Albatross and how her draft limited the surveys to offshore waters within the Bay. She was 234 feet and built expressly for the Fisheries Service in 1882, a substantial steam auxiliary square-rigged for sailing on both masts. (I find it appealing that at least part of the early monitoring work was done under square sail, the same technology that had opened the Bay to Europeans almost four centuries earlier in 1526!)
The first large-scale surveys were conducted under Lewis Radcliffe in 1915, 1916 and 1917, but were discontinued. They were resumed by Dr. R.P. Cowles from 1920–22.
The framework of stations they established was remarkably like the mainstem monitoring network in place today, with stations in transects laterally crossing the Bay and Potomac mouth in six places. A total of 30 stations ranged from the Virginia capes to the Patapsco River.
A summary of the entire data set was published in the early 1930s while Cowles was a professor at Johns Hopkins University in Baltimore. Their work, little known today, provides modern readers — struggling with many of the same interpretive problems — with an early if indistinct look at the Chesapeake in the first quarter of the 20th century.
Radcliffe’s and Cowles’ work included dragging a large number of trawls and net tows through the water to grab materials and organisms from the bottom. Their discoveries were many, including a few new species. Even with their discoveries, little was known about estuarine organisms at the time.
Among the Bay’s varied benthos, for example, Cowles wrote: “there is no proof from the data at hand that the degree of salinity is a factor governing the distribution of annelids (polychaete or segmented worms) in Chesapeake Bay.” The controlling osmotic role of salt is universally known today.
There were few historical references to sea nettles: one in 1750, another during the Civil War and a third group from 1899–1906. Cowles reports them anecdotally in the St. Mary’s River and 10 miles up the Severn in 1904–5. During the 1915–16 surveys, the net tows captured them from the Bay’s mouth to Sandy Point above Annapolis, and in July 1916, they were so dense that fishermen in the Lower Bay pulled their nets to avoid “nettle burn.”
Cowles’ and Radcliffe’s hydrographic survey work required hundreds of individual water samples that were collected using the “Green-Bigelow water bottle”: a sampler sent down open and that could be closed at a predetermined depth.
Temperatures were taken with “Negretti-Zambra reversing thermometers,” which captured at each deployment a single temperature reading at a desired depth when the device was tripped using a messenger weight sent down the cable. Half of the water sample was used for a plankton sample and another portion was returned to the laboratory, titrated chemically for chlorinity and converted to salinity using Knudsen’s tables. Their work produced thousands of data points covering about 640 stations over a period of five calendar years, certainly an impressive first look.
These studies gathered a great deal of plankton data, which suggests the Bay had significant spring and autumn phytoplankton blooms dominated by diatoms — microscopic plant cells with their living material enclosed in a hard silica case.
Interestingly, Cowles wrote that benthic — bottom dwelling — diatoms predominated, a condition echoing data from deep bottom cores of sediment from the colonial 16th–18th centuries, when clearer water conditions and vast beds of Bay grasses were believed to prevail.
There was a lull in summer plankton during which Cowles believed that dinoflagellates — microscopic plant cells capable of swimming with whip-like flagella — were growing on the decomposition products of earlier plankton growth.
Today, this is only part of the equation.
Plankton breakdown products are not only feeding dinoflagellate blooms, but the bacterial decomposition of their excess drives the summer exhaustion of oxygen in the Bay’s deep water.
The data showed that salinity was substantially higher in bottom waters — a situation Cowles called “katohalin,” and that this was accompanied by temperature changes which assured the density of bottom water was great enough to resist mixing with the fresher layer above.
Laborious successive deployments of the bottles and thermometers, done many times over 24 hours at several stations showed that the zone of rapid salinity and temperature change — what Cowles called a discontinuity — was relatively narrow. Today, this water column feature is called a pycnocline.
About 18 years before Radcliffe began this work, W. Bell Dawson, working in Canadian waters, had found that this vertical stratification of layers was accompanied by an upstream or countercurrent flow of saltwater along the bottom. This, confirmed by Cowles’ analysis in the Chesapeake, began the working out of characteristic circulation patterns in partially mixed estuaries.
In the early 1950s, Donald W. Pritchard at Johns Hopkins University described and published these dynamics in mathematical terms which subsequently led to many chroniclers claiming that he “invented” estuaries!
Cowles and Radcliffe were certainly well- acquainted with the Bay’s bathymetry, which had been laboriously sampled in the previous century using longboats and sounding leads, and assembled into excellent, beautifully drawn charts by the U.S. Coast Survey.
Cowles wrote clearly about the ancestral drowned Susquehanna River valley and took special note of the “deep holes along the eastern shore (which) are connected with each other by regions of greater depth than the average of the bay, so that there is a natural deep channel. … These deep holes are of special interest on account of their permanence, their comparatively rich and unusual invertebrate fauna, and their relation to fishing grounds.”
These deeps are today characterized by annual, persistent anoxia (lack of oxygen), which is a major feature of the eutrophic Chesapeake estuary. They are inhabited only temporarily in the cold months by an ephemeral few juvenile and opportunistic benthic species which are killed annually by warm weather anoxic conditions.
(There is a recurrent expedient of dumping millions of yards of waste material dredged from harbor navigation channels in these deeps. That action would preclude forever reestablishing the “rich and unusual invertebrate fauna” in a future Chesapeake where hypoxia might finally be controlled.)
It may be significant that while their presentation is not always clear, Cowles’ and Radcliffe’s crews did not appear to find anoxic sediments reeking with the hydrogen sulfide of decomposition which are so often encountered today in mainstem channels. Cowles describes “blue muds” varying “...somewhat in color from black to blue black to brown in the Chesapeake, probably depending on the amount of organic matter and sulphide of iron present.”
Consistency was not the same all over, and there was some “soft puddled mud” in places. They describe some sediments as “foul,” even while containing live worms. But, ordinarily, “the blue mud layer is not very thick except in certain regions, such as the mouths of rivers. Usually a sample cut out of the bottom to a depth of 2 or 3 inches shows a lower layer of sand, clay or shells...”
Cowles’ statement about rich and unusual invertebrate fauna in deep water is most provocative. The overall record of species taken during the survey is quite diverse, although many of the organisms came from relatively shallow water along the “wings” on either side of the main channel.
In cases where Cowles stated a depth, or a species came from a known station, and the specified date falls within the period when that area is likely to experience anoxia annually today, one can be pretty sure that those organisms are not there now in the summer. In the modern Chesapeake, summer oxygen generally declines rapidly below 6 meters.
Applying this criteria, we find some interesting occurrences: Among the benthos, the scaleworm Lepidonotus squamatus appeared down to 13 meters in July 1920. It was also found at 46 meters but records do not identify the station or the date. Bryozoans and anemones were fewer in the deep holes, although some occurred at deep axis Stations “R” and “S” well up in the mid-Bay region. The polychaete Nereis limbata, then thought to dwell only in mud was sometimes found at and occasionally below 15 meters. Gorgonians, or sea whips, Leptogorgia virgulata, were found in June at Station “I” as well as the hermit crab Pagurus longicarpus and Balanoglossus off the mouth of the Potomac. Nearby, in July 1920, were sponges, Tetilla laminaris at 10 meters and Microciona prolifera at 13 meters off Point No Point above the Potomac. At Station “R” off Barren Island, fragmental gorgonians occurred, and twice from August to October, the polychaete Priospio plumosa (which was just then being described as a new species) turned up. Anemones were nearby at 12 meters but not in the channel; Cowles suggests this was because that area lacked hard substrate for them to grow on. Pectenaria gouldii was off the Magothy at depths of 8–44 meters in 1921.
Cowles was eager to list as many organisms as possible in constructing an invertebrate fauna for the Chesapeake. Although he also recorded salinity and temperature, Cowles apparently had no inkling about the critical role of oxygen. It’s surprising that no measurements of oxygen, nor any measures of water clarity were ever made. They would have both been extraordinary in their usefulness for interpreting the times.
The oxygen method available to Cowles, and Radcliffe before him, was the Winkler method, which had been published in 1888 and was the method available to oceanographers and in laboratory physiology studies well into the 1960s. It is still a reliable and accurate means of calibrating polarographic dissolved oxygen “probes” and is widely used by volunteer monitoring programs in the Chesapeake and nationwide.
Winkler’s method combines additions of dissolved chemicals to quantitatively measure oxygen gas in water by releasing iodine in an equivalent amount, which could be titrated accurately to the smallest drop, with sodium thiosulfate.
Had the Cowles’ and Radcliffe’s surveys been continued, and if Cowles had known the value of augmenting hydrographic measures with dissolved oxygen, scientists might have documented the onset of regular summer anoxia decades before others observed its deep entrenchment. As it was, the first hints about declining subpycnocline oxygen did not appear until 1947, when the Chesapeake Biological Laboratory published Carroll Blue Nash’s work in the Lower Patuxent.
Nash’s first samples in 1936, about 14 years after Cowles’ last cruise, included dissolved oxygen titrations for both the surface and bottom. Over a 10-year period, Nash found that summer dissolved oxygen values at the bottom fell radically in the summer, sometimes to as low as 1.34 cc per liter.
His work was virtually lost for decades until University of Maryland researchers Don Heinle and Chris D’Elia found them on a dusty shelf. Arguments were framed that awakened society to the Bay’s increasing oxygen problems and linked them to the rampaging nitrogen loads which today are the prime focus of restoration efforts. Consistent monitoring of the kind Nash began certainly would have alerted managers two decades earlier.
When Pritchard and his colleagues began regular survey cruises along the Bay’s central axis during the 1950s, they identified summer anoxia as a regular feature, but it was many years before the likelihood of its increasing severity would emerge. Even this consistent chain of monitoring was broken by the dissolution of the Chesapeake Bay Institute and the scattering of its personnel, resources and data. Indifferent administrators at Johns Hopkins University were apparently unaware of the value to society that was being lost.
Would this knowledge, as a continuous record from 1915 — and the search for its causes — have alerted us to the Bay’s problems in time to rethink how the basin was developing? What might have been the implications for industry and agriculture, both rapidly expanding at the time?
We can only speculate on the answers to those questions, but we are wise to have sustained today’s monitoring programs, which are vastly superior to their predecessors, into their 17th year.
Although a difficult and expensive tool, effective, consistent monitoring is an irreplaceable insurance policy as we try to sort out improvements from declines in an environment where changes thrust us from years of massive floods, such as 1996, to droughts such as 1999. The utility of monitoring is amply underscored in the National Academy (of Sciences) Press’ report, “Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution." (See “Report traces most of coastal water’s ills to excess of nutrients,” October, 2000.)
The work done by Chesapeake monitors needs to be nurtured and sustained. Its value is inestimable for later generations of managers and must continue far beyond political terms of office or the tenure of personal careers. In the future as well as today, past will be prologue.
The author would like to thank the Maryland DNR and Bob Murphy of the Alliance for the Chesapeake Bay for their contributions.