What makes beach water brown

Rip currents do occur at the beach, and both these and the exceptionally wide surf zone — wider during south easterly winds in summer — can be observed from the mountainside on Boyes Drive. A rip current is like a hidden river flowing out to sea from the beach.

The Sydney Morning Herald has an excellent visual explainer of rip currents here. The head of False Bay where Muizenberg is situated is incredibly nutrient-rich, much of it thanks to urbanisation.

Many of these nutrients are technically pollutants, added to the river further upstream. The Cape Flats Waste Water Treatment plant at Strandfontein also discharges million litres of treated water per day under normal, non-drought circumstances via a canal onto Strandfontein beach.

This is essentially an artificial estuary for Zeekoevlei. This waste water has spent some time working its way through the settlement ponds at Strandfontein, but is nevertheless rich in ammonia and other nutrients, and Anaulus accumulations are a very common sight in the surf around this discharge point. The dunes that run along Baden Powell drive overlay a high water table, and groundwater seepage — specially during times of heavy rainfall — may also leach nutrients out of the ground and into the surf zone.

The meteorological conditions required for an Anaulus accumulation involve strong wind and a large swell. These act together to create rough sea conditions, which stir up the dormant diatoms from the ocean floor. The diatoms adhere to air bubbles in the surf zone, staying suspended in the water column, which is when you would notice the water turning brown.

Exposed to light, they awaken from their dormant state and start to photosynthesise, take up nutrients, divide and multiply. The presence of rip currents creates an onshore-offshore flow all along the beach. This forms a semi-closed ecosystem, and the diatoms are essentially trapped in gyres in the waves. Longshore currents that run parallel to the beach transport Anaulus cells out of the surf zone at one end, and bring fresh sea water in at the other end of the beach. It may seem surprising that anything manages to accumulate in the waves of a beach, but the surf zone is actually quite retentive, meaning that things that end up there often tend to stay there.

It must be discharged offshore so that it can disperse and mix with the surrounding water. This is deliberate, because of the constant presence and constant rate of division of the diatoms.

Well yes, in a way. But accumulations of Anaulus australis and related species have been observed and documented for well over years at suitable beaches around the world, and are a natural phenomenon.

Yes, we are providing more nutrients to the False Bay diatom population than they would otherwise have received without human settlement in the greater Cape Town area, but these accumulations would likely occur regardless.

They are certainly more intense now than they would have been in the past, but estuaries are nutrient-rich locations even when not surrounded by a large city. Furthermore, the water table is high on the Cape Flats, which would supply nutrients to the surf zone regardless of whether humans lived nearby.

Anaulus is in fact performing a vital and useful function by mopping up the excess nutrients that the city discharges in the ocean. The mass of diatoms — primary producers — also provides a food source to bivalves such as mussels, and other invertebrates.

We can be grateful that the excess nutrients that urbanisation directs towards the ocean at the head of False Bay leads only to accumulations of harmless diatoms, rather than to frequent occurrences of harmful algal blooms that can kill marine life and exacerbate respiratory problems in humans.

I did quite a bit of reading to research this post, but you can start with this paper for a description of the topographical characteristics of beaches where surf zone diatoms accumulate. The first few chapters of this Masters thesis also provide a good overall survey of what is known about surf zone diatoms. We built it that way. The color from the tannic acids is the least concerning thing about it, but it is polluted and dangerous.

Some of the brown color might be from dead algae. Both green algae and dead brown algae are things to stay away from. Wait until you read my next articles. I hope you like them. The next one has some really cool pics. What Boca does is impressive. You asked it yourself: What is making the water turn brown? That is the initial sign before your water becomes toxic. Come to Stuart and meet us, your northern neighbors.

Meet the fishermen, the small business operators, the small hotel owners, the River Keeper, the scientists, marine biologists and very concerned community that have experienced these outbreaks for years. There was a panel discussion, moderated by Maggy Hurchalla — one of nine members of the Everglades Hall of Fame — who rubbed elbows with the only other Martin County inductee, Nate Reed who passed away on July They control the canals, not what is in the water.

They are flood control. The North Fork of the St. Lucie River flows through the eastern portion of the city; a boardwalk is the only platform the general public has to see what is happening to the water other than a commercial tour boat. A local boat captain ceased operations of his guided eco tour of the river in when the enteric bacteria and fecal coliforms ruined his historical presentations; in six years he had over 15, people learn about our marine waterway system.

Boat owners can enter the C24 Canal or a few other boat launches. This city is known for golf courses — it is mostly land-locked. Hi Debra — I just spoke with Mark.

He clued me in on his perspectives on the problem. Thanks for pointing me in his direction. I greatly appreciate comments like that with the potential to lead to more article topics. I visited our world-class water plant, a place where our drinking water prepared for consumption and our wastewater is treated for discharging back out into the environment. The second part is where it gets really interesting.

I put this article on 4boca. Does our city make a point of bragging about its water handling excellence? Save my name, email, and website in this browser for the next time I comment. Sign in. Forgot your password?

Get help. Privacy Policy. Password recovery. Dead Reef Park. Your point please. Please enter your comment! Please enter your name here. You have entered an incorrect email address! Jason Pelish - October 5, 0. Local snorkeling fans have something new to be excited about: a new set of rocks to snorkel around at Red Reef Park. Let's go The interaction of these two currents brings nutrient-rich water from the deep ocean to the surface, providing an excellent environment for the growth of phytoplankton.

The distinct populations of phytoplankton in each current can be perceived as different colors. Recommended Articles. September 28, September 08, May 10, Episode 31 - Connected By Earth. April 28, Ask a Question. The turquoise swirls of the Malvinas Current are likely colored by a bloom of coccolithophorids. In the first image, a tendril of dark-green Brazil Current water is mixing with the lighter blue of the Malvinas Current, and in the second image, clearer water from the adjacent Atlantic Ocean is mixing with the Malvinas Current.

Coccolithophorids are phytoplankton that make microscopic spheres composed of calcium carbonate plates called coccoliths. The bright white calcium carbonate spheres excel at reflecting light, producing the milky turquoise-blue color of a coccolithophorid bloom.

As the coccolithophorids are dispersed and sink in deeper, clearer ocean water, the color of the water deepens to azure. This portion of the image features the light-brown, silt-laden water in the wide and shallow Rio de la Plata estuary, which lies just south of the city of Buenos Aires. The Rio de la Plata receives the flow of the Uruguay and Parana rivers, heavy with sediments eroded from the Andes Mountains.

As the estuary deepens into the Atlantic, the light-brown color darkens to a greenish-brown. This portion of the image shows the Bahia Blanca estuary, which receives the flow of several small rivers draining the southern Argentinian Pampas. Because these rivers carry less sediment than the larger Uruguay and Parana rivers, Bahia Blanca has clearer water, and the brown sediment color inland transforms to light green along the coast.

In this case, the color seen from space may also be influenced by the reflection of light from the shallow sea floor. East of the turquoise Malvinas current, the dispersed coccolithophorids in the current mix with the dark blue-black waters of the southern Atlantic Ocean. This isolated patch of phytoplankton appears greenish-white, due to a combination of light reflection and light absorption. This spiraling blue-green section of the Brazil Current is evidently populated by a different species of phytoplankton than the bright coccolithophorids floating just to the east, as indicated by its distinctly different color.