Tag: adventure trip

Beach Geomorphology on Deer Island

Figure 1: Beach profile on Deer Island spit.

The western end of Deer Island extends a white, sandy, artificial, spit that partially covers the first of a series of riprap breakwaters that protect the waterfront development of the city of Biloxi. Although we’d landed there to pick up garbage as part of our coastal science camp, the beautifully developed beach profile was worth a few minutes.

Figure 2: Narrow beach typical of the east-west trending shorelines that are not exposed to the direct force of the waves.

The spit curves just ever so slightly northward, so it feels more of the direct force of waves blown all the way along the length of Biloxi Bay. The combination of unvegetated sand and stronger waves makes the beach along the spit looks very different from the beaches that parallel the shore. While the parallel beaches on Deer Island are covered in grass almost to the water’s edge (Fig. 2), the spit has a much wider beach, with a nicely developed sandbar protecting a shallow, flat-bottomed, water-saturated trough behind it (Fig. 1).

While the white beaches are pretty (that’s why they imported this sand after all), there are a number of fascinating features in the trough.

Figure 3: On our Natchez Trace hike we found it quite easy to stick fingers into the red precipitate at the bottom of the stream.

The first, and most obvious question is, why the reddish-orange color in the fine grained sediment at the bottom of the trough? A microscope and a little geochemical analysis would be useful here, however, lacking this equipment, we can try drawing parallels with some of our experiences in the past. In fact, we should remember seeing the same color in some of the streambeds when we were hiking in Natchez Trace State Park in Tennessee (Fig. 3). My best guess at that time was that the red was from iron in the groundwater being oxidized when it reached the surface.

Figure 4: The rich black of decaying organic matter, sits just beneath the rusty-orange surface sediement.
Figure 5: Green, organic matter, freshly deposited at the edge of the trough. If it decays while saturated with water it will turn black. Note also the splay of white sand at the top of the picture.

This is probably not a bad guess for the red in the trough as well, since there is some fresh groundwater discharge from the shallow watertable on the island. However, I suspect that the story is a bit more complex, because the rich black color of the organic matter just beneath the surface (Fig. 4) suggest that the shallow water and surface sediment in the trough is lacking in oxygen. On the other hand, it’s not uncommon to have steep geochemical gradients in boundary environments like this one.

The physical and geochemical gradients extend horizontally as well as vertically. At the edges of the trough the organic matter just beneath the surface is green, not black (Fig. 5), because this is the color of the undecayed algae.

At the seaward side of the beach, the waves of Biloxi Bay lap against the sand bar. When the tide rises, and the wind picks up, these waves wash over the crest of the sand bar pushing water and sediment over the top into trough. When the sand washes evenly over the top it creates thin layers (possibly one layer with each high tide). If you cut into these layers you’ll see little the laminations in profile, which, because the layering is close to horizontal, look like the lines of topography on a map (Fig. 6). When the waves wash over small gaps in the sandbar the sediment it transports is deposited in a more concentrated area – these are called sand splays – that overlap and cover some of the fine-grained, orange sediment at the edge of the trough. These are both two of the small ways that the sand bar moves, slowly pushing inland.

Figure 6: Sand splay and laminations on the landward side of the sand bar. The laminations are created by even overwash of the sandbar, while the splay is the result of more concentrated flow.

Bioturbation

The features on the bottom of the trough are a quite interesting because of the observable effects of bioturbation (disturbance by organisms) (Figs. 7, 8 & 9).

Figure 7: In close-up, the holes of the crabs and the mixture of colors looks like an arid, volcanic landscape photographed from space.
Figure 8. Digging deep beneath the orange surface sediment, small crabs create mounds of white sand.
Figure 9. Footprints of predators. Paleontologists use features like these that are preserved in rocks to discover interpret what the relationships between organisms was like in the past.

It Takes a Long Time to Go Away: Collecting Garbage on Deer Island

Collecting anthropogenic debris on the beach.

Plastic bottles take 100 years to break down; styrofoam cups – fifty years; aluminum cans – 200 years; glass bottles, which are made of silica, just like the beach’s white sand – who knows. So we took a little time out of our adventure trip to collect anthropogenic debris as we walked along the beach on Deer Island.

Leather (shoe) - 50 years.
Plastic bags - 10 to 20 years.
Styrofoam cup - 50 years.
Plastic bottles - 100 years.
Tin cans - 50 years. Aluminum cans - 200 years.

We picked up stuff on our way out, so we were able to enjoy the fruits of our labours on our walk back to the landing point.

The beautiful beach cleared of garbage.

Note

The degradation times for marine garbage can be found on the SOEST website, but That Danny has an interesting compilation of data that tries to reconcile the different degradation times you can find on the web.

Biota on the Deer Island Beach

Comb Jellies are pretty and not poisonous.

We were there to collect garbage, but we found lots of life on the Deer Island part of our adventure trip to the gulf.

Ecotones, the boundaries between different environments tend to be rich in biological diversity.
Hermit crabs were everywhere.
Comb jelly in the hand.
Ospreys nest on the island.
Barnicles on a stick.
Tiny crab.
There were fewer actual snails than there were hermit crabs.
Dolphin in the boat's wake.

Collecting Garbage on the Beach: The Trip to Deer Island

To the left, a long, narrow, lightly-wooded island. Skeletal trees, dying on the upwind end; drowned by the attrition of the waves. To the right, a narrow, eager, urban strip. Hotels and casinos, pressing against the water’s edge; vying for access to the white sand beaches and gentle waters of the sound. Such different places on either side, yet the one on the right is the reason we’ve come to the one on the left. We’re here as part of our Adventure Trip to pick up any artificial debris that’s managed to float across the sound and collect and contaminate the quiet, isolated beaches of the island.

We’d gotten on a pontoon at the research lab right after breakfast, so the early adolescents were still a little groggy. Our vessel’s captain asked a question about team mascots which promptly woke up approximately 63.64% of the class, and served as a topic of conversation for the twenty or so minutes it took to get to the drop-off point on the west-north-western end of Deer Island.

Shrimp boat caught in the act of deploying its nets.

Mostly unobserved by my busy students were the half dozen shrimp boats casting their nets in the sound. Long, spider-like, almost robotic arms spread out from the vessel to lower the nets. It’s quite an impressive sight. Commercial shrimping is a major industry all along the Gulf coast.


Deer Island (and its hike). View Coastal Sciences Camp, Gulf Coast Research Lab in a larger map

Mostly dead trees.

The island itself is long and thin, wedge shaped, no more than a couple hundred meters at its widest at the eastern end, but thinning to less than 100 meters to the west. Although wider, almost all the trees seem to have died on the eastern end. Then there is a gap and the trees are mostly alive. Looking at the satellite image, you can see a clear channel cutting through the island. From the image, I’d guess the channel is tidal, with water moving back and forth, filling and draining the sound with each cycle of the tides. The sediment deposited in the quieter waters of the sound (to the north) seem to be forming a small, white-sand delta; the equivalent deposits on the south are probably washed away by the longshore current pretty quickly since that shore is exposed to the wind and waves.

Deer Island is not an active barrier island: twelve kilometers to the south, Horn and Ship Islands do that job today. However, given the shape of Deer Island, it may have once been a barrier when the coastline was further inland. This is all part of the coastal plains deltas, which includes the Mississippi Delta and smaller rivers. These rivers transport sediment from the mountains inland and deposit them in the ocean, gradually building out the land. As the deltas build out, the barrier islands also push out to accommodate them.

Scrambling for dry land. Note the rich, black mud.

The pontoon pulled up on a broad, sandy beach then retreated to deeper waters where the fishing is better. The white sand beach we landed on was an artifice, just like the East Beach Drive beach we’d walked the day before. Our first steps betrayed the secret. Breaking through a thin cover of sand, we sank knee-deep into a rich black mud that’s the natural sediment in a quiet waterway like the sound.

Our guide, on the other hand, seemed to have a preternatural ability to avoid sinking into the mud, or even getting her feet wet, or even touching the water.

Stephanie, our guide, carefully takes her first few steps off the boat. (no photoshopping was involved in the creation of this image).

References

The first image was distorted using a four point distortion method with ImageMagick.

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> convert sc-deer-island-1841.jpg -matte -virtual-pixel transparent -distort Perspective ‘0,0,0,0 0,664,0,664 1000,0,1000,200 1000,664,1000,564’ tst.jpg

Squid Dissection

Observing external features; finding the beak.

To follow up my own attempts at a fish anatomy lesson, I asked the people at the Gulf Coast Research Lab’s Marine Education Center to include a dissection in their program for our Adventure Trip. They chose squid.

Squid are nice because they’re mostly soft tissue and the organs are fairly easy to identify. They’re also quite charismatic, which piqued the students’ interest. These squid were going to be used as bait, so I didn’t feel too badly about using them for science.

Squid and reference diagram.

Once again, our guide, Stephanie, was an excellent teacher. A good time was had by all, even though it was a bit gruesome.

An excised beak.

I would have liked to have a little more time to draw some diagrams, but I don’t think my students would have had the patience. It was the Adventure Trip after all, and they’d much rather spend the time outside.

As for the future, I like this note about squid dissection:

… this … is a tactile experience. You may want to explore this aspect through sensory activities, written descriptions, poetry, and/or artwork. Encourage students to experience the many textures found inside and outside the squid’s body. Moving fingertips along the suckers is suggested as well – the suckers do not scrape or hurt if you are gentle with them.

–Center for Educational and Training Technology, Mississippi State University: Squid Dissection

This quote comes from a Mississippi State website, which also has a great set of calamari recipes in addition to dissection instructions. I’m always in favor of an interdisciplinary approach; food-preparation rather than purely dissection.

Finally, the University of Buffalo’s Biology 200 class has some excellent, labeled pictures, for reference.

Blind Sampling of the Subsurface

Extruding sediment from the corer into the sieve. Dashed lines indicate where the piston and metal rod extend inside the barrel of the corer.

On the first morning of the Coastal Science Camp, between dip netting and seining at the estuary, we tried sampling beneath the seabed using a little coring device which I seem to have to forgotten the name of.

Some students were quite excited about the chance to sample beneath the surface of the sediment. Student displays the sampling device is in his right hand.

Usually, they can see the little holes in the seabed where the benthic macrofauna live, but not this time. All the sediment pouring into the Mississippi Sound from this spring’s swollen rivers had made the waters too turbid to see through. So we were coring blind.

The corer is simply a metal (stainless steel) barrel with a rubber piston inside. The piston is connected to a handle at the top with metal rod. To sample, you put the tip of the barrel at the sediment-water interface and push the barrel into the sediment at the same time holding the handle steady to keep the piston from moving into the sediment. Holding the piston steady provides a little suction on the inside of the barrel, which helps the barrel move into the sediment, and keeps the sediment in the barrel when you pull it out. However, it does help to put your hand on the bottom of the barrel as soon as possible to keep the sediment from falling out, even if that means sticking your hand into the sediment itself.

Keeping you hand on the bottom of the barrel keeps the sediment from falling out before it gets to the sieve.
Vague layering is visible in the sediment.

Once you’ve recovered the sediment, you extrude it into a sieve. Sometimes you can see a little layering in the extruding sediment, but we did not take the time to try to interpret it since our focus was on finding benthic fauna.

The sieve’s mesh is pretty coarse, so anything sand sized or smaller is washed out as you gently rock it back and forth in the water. We did not find much. Mostly small pebbles. Without being able to see the seabed our sampling pattern was pretty random.

Small pebbles in the sieve.

The more persistent groups (the class had been broken into groups of two or three) did find a couple things, including a polychaete, which is a segmented worm.

A polychaete.

They also turned up a small, clawed, lobster-like organism:

We also found the burrow of an unknown organism, surrounded by a clayey cast. It looked very much like some of the fossilized burrow casts we saw at Coon Creek.

Burrow, with surrounding cast.

This type of sampling was not everyone’s cup of tea, however. Fortunately, the water was shallow and warm, so a good time was had by all.

Some groups were less successful at finding benthic macrofauna than others. They had other things on their mind.

Longshore Drift and Pufferfish

A groin strains to hold back the longshore drift. It is, as always, only partially successful.

It was about 1.5 kilometers from the Research Lab to the estuary where we spent our first morning sampling (overview of the trip is here).

Elevated beach house.

Walking along the beach to get there, we could see the beach houses to the right of us, across the narrow road of East Beach Drive, standing tall on columns to keep them above the reach of the storms. According to Stephanie, our guide, the storm surge from Hurricane Katrina in 2005, reached awfully close to the tops of the columns. The research lab, which is not elevated, lost an entire building to that hurricane. Indeed, much of the coast is still recovering from Katrina’s damage.

The white sandy beach, on the other hand, looked beautiful, which was a bit odd. After all, how did it survive the storm? Furthermore, when you think about it, this beach is located behind a string of barrier islands, which protect the coast from the full force of the waves coming out of the Gulf of Mexico, so how come there is enough wave energy to maintain a sandy beach. The relatively calm waters should allow finer grained sediment, like clay and silt, to settle out, and this area really should be a marsh. The answer, it seems, is that this is an artificial beach. Every few years, thousands of tons of sand are dumped along the coast to “replenish” the beachs.

Without beach replenishment the beaches would revert to salt marshes like this one.

This coastline really should be a tidal marsh, like the one we found when we got to the estuary. These Gulf-coast salt-marshes are fronted by a relatively short version of smooth cordgrass (spartina alterniflora), backed up by the taller, and more common black needlerush (Juncus roemerianus Scheele) .

Longshore Drift

Now, if this is a low-energy environment that allows silt and clay can settle out of the water column, where does the sand go so that it has to be replenished every so often? It is gradually moved along the coast by longshore drift.

Longshore drift moves sand along the coast in the direction of the wind. Image via the USGS.

Waves hit the beach at an angle. As they break, the turbulent swash pushes sand up the beach at the same angle as the movement of the waves. As the wave retreats, the backwash, drawn by gravity, pulls sand perpendicularly down towards the water. The net effect, is that sand gradually moves down the coastline with each swash and backwash of the waves.

Since dumping tons of sand is expensive, engineers try other things to prevent the sand from running off down the beach. Someone, a very long time ago, had the great idea to build a wall sticking out from the beach to impede the sand in its unwanted migration. This type of wall is called a groin (or sometimes a groyne in polite company), and it does stop the sand. In fact, the sand builds up on the upwind side of the groin. Unfortunately, it does not stop the longshore drift on the downwind side, and that results in the erosion of a bay on that side.

A groin impedes longshore drift. Note that the waves approach the beach at an oblique angle.

Pufferfish

Beaches are also great places to find random things washing up. We lucked upon an unusually large pufferfish (family: tetraodontidae). It was quite puffed up. It was also quite dead.

Pufferfish.

Pufferfish are famous for being extremely poisonous. According to the National Geographic page on pufferfish, their tetrodotoxin over a thousand times more poisonous than cyanide, and there is no known antidote.

Seining in the Sound

Setting up the seine.

After surface sampling with the dip nets, and subsurface sampling with the little corers, we tried sampling the water column using a small seine.

Seining requires teamwork, and I was pleased to see everyone working well together, focused on the job at hand.

Working together to bring in the catch.

Hauling on the nets, with the smell of salt in the air, resurrected long neglected memories of fishermen at work on tropical, Atlantic beaches. Back then they were going after fish for the market, here, with our much finer meshed net, we were looking for anything interesting in the water column.

Examining the catch.

Everyone got touch a ctenophore (comb jelly), which I will note is not a jellyfish, and is also not poisonous.

If you look carefully you can just make out a comb jelly in the jar.

Students also had a chance to hold a croaker (a fish of the family Sciaenidae), and feel it croak.

Feeling the croak.

Our guide was great. She was quite knowledgeable about the fauna we ran into, and very good at sharing information.

Stephanie T. pointing out the finer points of piscine morphology.

Interestingly, we were not the only ones out seining that morning. There was a small group from the research lab looking for skates for a research project. I think they said that this was their third time out looking, but like us, they did not find any elasmobranchs (not counting the one dead specimen we ran into while dip netting).

Remains of a skate, lying in the grass at the edge of the beach.