FACTORS OF SWAMP SPATIAL DISTRIBUTIONS

 Regular readers of Swamp Things (both of you) may recall a post a few months back on The Factors of Swamp Formation. In it I applied the factorial conceptual model first developed in soil science and later applied in many other fields (especially ecology) to swamps and other wetlands. The follow-up was just published in the journal Hydrology. I initially submitted it with the "factors of swamp formation" title to resonate with the well-known factors of soil formation concept. However, reviewers pointed out, correctly, that the work deals more with spatial patterns and geographical distributions than with formation. 

The abstract is below:

Abstract

A state factor model of bottomland hardwood swamp formation is applied to a lower coastal

plain river in North Carolina, U.S., to explain variations in wetland hydrological, ecological,

geomorphological, and soil characteristics. Swamps and wetlands are a function of the

interacting influences of the state factors of climate, topography, hydrology, vegetation,

fauna, soils, geomorphic setting, and time. Five classifications of swamp and related

environments were applied to the study area, with the categories present determined

based on fieldwork. For each classification, the implicit, embedded state factors were

identified from the classification scheme itself. Relevant environmental gradients for the

study area were identified, and a spatial adjacency graph for the study area was developed

for each classification. The ability of the environmental gradients to explain the spatial

complexity of the pattern was assessed using spatial adjacency graph (SAG) analysis. All

the classification criteria are associated with the proposed state factors. SAG analysis

shows overdetermination, indicating that known gradients of causal factors are sufficient to

explain the overall pattern of spatial contiguity and that single-factor models of change are

not sufficient at the local scale. Results confirm studies showing that responses to seilla-level

and other changes are spatially patchy.

The article is open access, and you can get it via the link embedded in the citation:

Phillips, J.D. 2025 The factors of swamp spatial distributions. Hydrology 12, 332. https://doi.org/10.3390/hydrology12120332

Below, just for the heck of it, a couple of pictures from a recent paddling expedition on some anabranches and lakes of the Little Pee River, South Carolina. Though it's a bit hard to pick out at first, the top one shows a swamp tupelo (Nyssa biflora) growing right up on the root crowns of two large baldcypress (Taxodium distichum). The bottom photo is one of many cool looking cypress trees in the area. 

BACKWATERS, MUCKS, & PEATS

 In honor of World Soil Day (December 5), a post about swamp soils, even though the theme this year is "Healthy Soils for Healthy Cities." 

In 1984, the great soil geomorphologist Raymond Daniels and colleagues at N.C. State University published a bulletin for the N.C. Agricultural Research Service called Soil Systems of North Carolina. In it, they noted that the Dorovan soil series, an organic muck or mucky peat found along the lowermost reaches of coastal plain rivers, likely marked the soil effects of rising sea-level gradually encroaching upstream. I took a closer look in the field, and at soil surveys from the region, and decided they were on to something. I first looked into this from the other direction, so to speak, investigating the extent to which floodplain sediments in the lower rivers is derived from the upstream, Piedmont portion of rivers draining to the Carolinas coast (spoiler for the roughly 8.3 billion people who have not been following my work for the past 35 years: very little Piedmont sediment makes it to the lower rivers). Below is a map from a 1992 paper on the subject. The soils marked as "coastal" are those organic soils. 

I revisited this in the 2020s in investigating various impacts and indicators of the upstream effects of sea-level rise on coastal plain rivers in South Carolina, North Carolina, and southeastern-most Virginia. I wanted to know how the upstream limit of the organic soils compared to that of other indicators. And more specific to the soil issue, a key question was how a river, swamp, or floodplain transitions--apparently relatively suddenly in some cases, judging from stratigraphy--from a muddy or sandy, mineral-dominated state to one that is overwhelmingly composed of organic matter?

Soil map showing transition from mineral Chastain soil series (symbol Ch) to the Dorovan mucky peat (symbols Dk, Do) along the Roanoke River near Williamston, N.C. From SoilWeb (https://casoilresource.lawr.ucdavis.edu/gmap/)

The three main soil series involved are the Dorovan, Hobonny, and Chowan series. The Dorovan and Hobonny differ only in their acidity; the Chowan series occurs where recent mineral deposition has buried the organic soil. 

Example profiles (from SoilWeb). The layers labelled with an "O" are dominantly organic material, with the "a" indicating highly decomposed material. 

An area of Hobonny soils, Thoroughfare Island, Waccamaw River near Conway, S.C.

In this study I found that the floodplain organic soils occur well within the areas influenced by coastal backwater effects. 

Maximium distance upstream from the head of the estuary of organic floodplain soils and three other indicators of coastal backwater effects on 20 rivers (from Phillips, 2024). 

I was able to work out a sequence of changes, as shown below, with the transition to organic soils highlighted. The short version is that the hydraulic effects of sea-level encroachment both inhibits downstream transport of mineral sediment, and increases the frequency and inundation of floodplains. The latter promotes the deposition of water-transported organic matter, and due to the fact that the vegetation is adapted to wetness, does not inhibit biomass production and litterfall from floodplain plants. The wet, anaerobic environment inhibits organic decomposition, and the organic material accumulates.

Organic matter and mud deposition along the Trent River, North Carolina.

Dorovan soil along the Black River, North Carolina.

The diagram below is a more detailed look at how the formation of the floodplain Histosols fits into the various changes now occurring as sea-level inches its way upstream. 

Studying soil geography and transition problems like this could shed some light on wetland evolution and development, the little-understood dynamics of fluvial-to-estuarine transition zones, and sea-level impacts on rivers. The areas characterized by Dorovan and similar soils are part of landforms and ecosystems that have very high values for wildlife habitat, flood and storm protection, water quality, and recreation. They are also highly vulnerable not only to sea-level rise, but also rampant land development, in some cases at a nearly crazed pace (see Horry County, South Carolina for instance). While the wetlands themselves may be protected from the excavators and bulldozers, the adjacent wetlands are subject to their adverse impacts on water quality, habitat and hydrological connectivity, and space for migrating in response to sea-level change. The mineral-to-muck (or peat) shift is also an example of a system transition that may represent, and shed light on, the broader study of regime shifts and tipping points.

References:

Daniels RB, Kleiss HJ, Buol SW, Byrd HJ, Phillips JA. 1984. Soil systems in North Carolina. Raleigh (NC): North Carolina Agricultural Research Service. Bulletin 467. 77 p.

Phillips, J.D. 1992. The source of alluvium in large rivers of the lower Coastal Plain of North Carolina. Catena 19: 59-75. 

Phillips, J.D. 2024. Sequential changes in coastal plain rivers affected by rising sea-level. Hydrology 11, 124.

VITAL SIGNS

 I have reported in several previous posts about the effects of climate change on bottomland hardwood swamps of the southeastern U.S., including sea-level rise (SLR1, SLR2, SLR3), fire regimes, and  storms.

Swamps, like this one along the Waccamaw River, S.C. are at risk from climate change--just like the rest of the planet.

The Sixth State of the Climate report was recently released, and it makes for scary reading. The first paragraph is: 

We are hurtling toward climate chaos. The planet's vital signs are flashing red. The consequences of human-driven alterations of the climate are no longer future threats but are here now. This unfolding emergency stems from failed foresight, political inaction, unsustainable economic systems, and misinformation. Almost every corner of the biosphere is reeling from intensifying heat, storms, floods, droughts, or fires. The window to prevent the worst outcomes is rapidly closing. In early 2025, the World Meteorological Organization reported that 2024 was the hottest year on record (WMO 2025a). This was likely hotter than the peak of the last interglacial, roughly 125,000 years ago (Gulev et al. 2021, Kaufman and McKay 2022). Rising levels of greenhouse gases remain the driving force behind this escalation. These recent developments emphasize the extreme insufficiency of global efforts to reduce greenhouse gas emissions and mark the beginning of a grim new chapter for life on Earth.

The report, subtitled "A Planet on the Brink", is available here and a news article about it from the American Geophysical Union is titled "Our Planet's Vital Signs are Crashing."

Meanwhile, in MAGAworld and Trumpistan . . . . 

GHOSTS IN THE ESTUARY

As sea-level rises, as it has been throughout the Holocene, and now rises faster due to human-accelerated climate change (yes, MAGA-world, that's a fact), bottomland hardwood swamps near the coast are being converted to oligohaline* and brackish marshes. As water levels rise, trees that can't tolerate regular flooding and constantly saturated soils die off. Then, as saltier water intrudes, trees that can tolerate being wet all the time but cannot tolerate salinity die off. This is creating so-called "Ghost Forests" (see my earlier Ghost Treespost). Generally the last tree standing, except for a few salt-tolerant shrubs and some holdouts on isolated higher spots, is baldcypress (Taxodium distichum) which can tolerate a little bit of salinity, which swamp tupelo and water tupelo (Nyssa biflora, N. aquatica) cannot. Baldcypress wood is famously decay-resistant; and the white trunks of dead trees are called ghost cypress. 

Oligohaline marsh and ghost cypress, Upper Broad Creek (top) and Cahoogue Creek (bottom), North Carolina.

You can see this happening throughout the southeastern U.S.A. coastal plains, but the general swamp-to-marsh conversion has been going on, albeit more slowly (see How to Drown a Swamp), for a long time. The evidence is under, or just above the water--stumps and roots of bald cypress at the edge of the marshes, with no living (and often no upright dead) cypress anywhere close by.

Baldcypress stump, Hancock Creek, N.C.

Cypress wood is renowned for its decay resistance, which is attributable largely to an oil called cypressene. In a recently-deceased cypress trunk, log, or root, the bark and sapwood decompose fairly rapidly. The heartwood, however, can persist for very long periods, particularly underwater, or buried in wetlands (fungi and insects can eat away some of the heartwood, creating tree cavities and some interesting patterns in the wood, such as sought-after "pecky" cypress). 

Remnants of a cypress stump adjacent to black needlerush (Juncus romerianus) marsh, Upper Broad Creek

How long is very long? Good question. There exists a cottage industry for lumber from cypress "sinker logs." From the 1880s to about 1920, a lot of virgin and old growth cypress was logged in the south, and was typically dragged from the swamps to canals, creeks, and rivers to float in log rafts to market. Some of the logs sank (one source estimates 10%). Because sinkers were difficult and expensive to recover at the time, nobody did. But in the late 20th century it was realized that these often huge, high-commercial-quality logs--with the heartwood typically not noticeably decayed--were worth recovering. Most of this activity is in the Gulf Coast states, but at least one operation is going on the Cape Fear River, N.C. (https://www.oldgrowthriverwood.com), and another in Charleston, S.C. (https://www.facebook.com/HeartwoodSouth/). Obviously cypress wood can last for >100 years underwater.

Sinker cypress wood for sale at Heartwood South

Ancient buried cypress wood is called "subfossil" rather than fossil because the heartwood is preserved more or less as-is (or as-was), and has not been fossilized by mineral replacement. Buried subfossil cypress has been reported in the southern U.S. since the 18th century. Sand mines along the Pee Dee and Lynches Rivers, S.C. have uncovered subfossil logs roughly 12 m below the ground surface, up to 2.4 m in diameter and up to 29 m long (Stahle et al., 2005). Researchers from the University of Arkansas Tree Ring Lab who studied the logs reported that other hardwood logs were also present, but none as well preserved as the Taxodium distichum. Radiocarbon dates indicate their ages range from about 25 to 45 thousand years old. The report also reviewed other accounts of subfossil cypress, including stumps in growth position with roots and knees still attached uncovered by 20th century construction in Washington, D.C., estimated to be about 100 ka. Rooted cypress stumps and fallen logs exposed along the Intracoastal Waterway in Horry County, S.C. are believed to date to 125 to 135 thousand years BP. There's more about subfossil cypress logs and what can be learned from them in Stahle et al. (2012). 

Along eroding shorelines of the Neuse River estuary, N.C., a swamp paleosol is exposed with cypress roots and stumps in growth position. This paleosol is under the ~200 ka Flanner Beach formation and is at least that old. It overlies the James City formation, which may be up to a million years old, but is generally thought to be about 700 ka (Miller, 1986a; 1986b). 

Without radiocarbon dating the age of the underwater marsh edge cypress cannot be determined, but we can say they could be very old. My guess is less than 4 ka, which is about the time the modern estuaries of the Carolinas became established. 

It is not easy, at least if you are no better a photographer than I am, to get good pictures of the underwater cypress, but below are a few attempts. All these examples are adjacent to brackish marshes with no trees nearby. They are all from tributaries of the Neuse River estuary, not because that's the only place this is happening, but because that's where I live and therefore kayak a lot. Early 20th century records of the U.S. Army Corps of Engineers dredging operations in the Pamlico River at Washington, NC, report encountering in situ cypress stumps at the bottom of the river, for one example. 

Portion of a submerged cypress stump, Goose Creek, Pamlico County, NC

Cahoogue Creek, NC

Upper Broad Creek, NC

A synthesis of Holocene, recent, and predicted future sea-level rise for the N.C. coast was produced by Kopp et al. (2015). Over the past 11 ka, the region experienced episodes of RSL (relative sea-level) rise acceleration and deceleration, but no periods of fall or stillstand. RSL reached to <10 m below modern levels by about 2000 BCE (or about 4 ka BP), when modern estuaries became established in roughly their modern locations. My guess is that at about that time some of the tributaries to the Pamlico Sound estuary were flanked by bottomland hardwood cypress-tupelo swamps. As RSL continued and continues to rise, salinity increased, first killing off the tupelo and other salinity-intolerant trees. In addition to dying sooner, the wood of these trees is less decay resistant than cypress, the last canopy-size tree to go. Tributaries such as the ones where pictures above were taken first saw formation of ghost forests and marsh conversion, eventually reaching a point where nothing is left of the cypress but a few snags (standing dead trees), stumps, and submerged roots and stumps. That process is ongoing and will continue and probably accelerate. Whether there is a net loss of bottomland hardwood swamps will depend on the extent to which they can expand along their inland and upstream margins. In terms of marsh area, the swamp-to-marsh conversion is offset by erosion and drowning. In most areas, including the Neuse River, there has been a net loss. 

*Salinity between 0.5 and 5.0 ppt. Fresh water is <0.5; ocean water is 33 to 35 ppt. 

References cited

Kopp, R.E. & 3 others. 2015. Past and future sea level rise along the coast of North Carolina, USA. ClimaticChange 132, 693–707. 

Miller, W.M., III. 1986a, Community replacement in estuarine Pleistocene deposits of eastern North Carolina. Tulane Studies in Geology & Paleontology 19, 97-122. 

Miller, W.M., III. 1986b. Paleoecology of benthic community replacement. Lethaia 19, 225–231. 

Stahle, D.W. & 3 others. 2005. Ancient Baldcypress Forests Buried in South Carolina. Tree Ring Laboratory, Dept. of Geosciences, University of Arkansas.

Stahle, D.W. & 9 others. 2012. Tree-ring analysis of ancient baldcypress trees and subfossil wood. Quaternary Science Reviews 34, 1-15.

My own related research

Phillips, J.D. 2024. Sequential changes in coastal plain rivers affected by rising sea-level. Hydrology 11, 124. 

Phillips, J.D. 2024. Ghost cypress as indicators of sea-level rise in the Neuse River, North Carolina. Wetlands Ecology and Management 32, 287-302. 

Phillips, J.D. 2023. Landscape change and climate attribution, with an example from estuarine marshes. Geomorphology 430: 108666.

Phillips, J.D. 2018. Environmental gradients and complexity in coastal landscape response to sea level rise. Catena 169: 107-118. 

Phillips, J.D. 2018. Coastal wetlands, sea-level, and the dimensions of geomorphic resilience. Geomorphology 305: 173-184.

GAR TALK

 On recent paddle up Tranters Creek near Washington, NC, the water, particularly in certain reaches, was churning with longnose gar surfacing (often called rolling) and leaping. It was a beautiful day on the creek, and I was reporting on it to my wife Lynn, who was not able to accompany me. When I indicated that I wished she had been there, she indicated that she had no interest in paddling through "gar soup," as I called it. She finds them "icky," and referred to them as primitive, unevolved, gill-less, top-breathing bottom feeders (OK, I am paraphrasing and embellishing here). Though I have nothing against gar I did not argue as I thought it was not an inaccurate characterization.

Gar party on Tranters Creek, NC

But I was wrong.

Longnose gar (Lepisosteus osseus) are indeed often described as primitive, because they have retained some primitive features, such as a spiral valve intestine and ganoid scales. They are olive brown to green in color, and their scaly armoring, torpedo shape, and long, toothy, spear-like snout do make them look like unevolved Jurassic killing machines. It seems they have been around for at least 100 million years, which would place them in the Cretaceous (younger than Jurassic but still dinosaur times), but in the U.S. fossils date only to the Pleistocene. 

Longnose gar in the N.C. Aquarium at Fort Fisher

Unevolved, they are not; they are actually highly adapted to their habitats. They are indeed gill-less. Instead they have a swim bladder that allows them to breathe air or water, which in turn affords them success in waters with low dissolved oxygen (DO), a frequent hazard for fish in the estuaries and swamps of the southeastern U.S. Their surfacing is the air-breathing part, and when they are churning the water as they were recently on Tranters Creek (I have seen similar gar parties in other creeks and swamps) it probably indicates low DO. Longnose gar are not bottom-feeders, or at least not exclusively or primarily. They generally eat small fish, and occasionally crustaceans and insects, wherever they find them. 

Longnose gar distribution in the U.S.A.

The species is mostly freshwater, but has been found in salinities up to 31 ppt, nearly that of ocean water. They are quite common in estuaries of the Pamlico-Albemarle Sound system, where they come out of the freshwater to feed on menhaden. They are found in lakes, ponds, swamps, and slow-moving rivers and creeks. 

                                                    Longnose gar from eastern N.C.

Fun gar factoids:

•The species was first named (though the genus was later renamed) by Carl Linnaeus, the father of biological taxonomy, in 1758. The name Lepisosteus osseus is derived from lepis (Greek for scale) and osteos (Latin for bony). 

•The North Carolina record for longnose gar has been broken twice so far in 2025, first in the Intracoastal Waterway near Coinjock, and then in a quarry pond near Maysville. The world record (25.5 kg) was caught by a bowfisher on Lake Palestine in east Texas. 

•Longnose gar can reach 2 m in length. The ones I see in the swamps of the Carolinas are generally in the 0.5 to 1 m range. 

•Longnose gar are known to breed and hybridize with the even bigger and scarier looking alligator gar (Atractosteus spatula), but that only happens in the Gulf Coast and lower Mississippi/Ohio River valleys. Alligator gar are not found along the SE coast. 

87.5 kg alligator gar from the Trinity River, Texas (https://www.reddit.com/r/Fishing/comments/13n2cte/alligator_gar_193_lbs_trinity_river_texas/#lightbox)

More information at animalia.bio.